BUG: Using categorical dtype in read_json
Pandas `read_json` ignores `category` dtype. This fix is need to using `category` in `read_json`. 
Example: `pd.read_json(filename, lines=True, dtype={'ColumnName':'category'})`.

fyi #21892

Hello @anki-code! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-03-06 18:11:31 UTC This needs tests - should always be the first part of any PR # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=h1) Report
> Merging [#25573](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3e652ac565e054b763ccbe23006c02704f6cd1b1?src=pr&el=desc) will **decrease** coverage by `49.54%`.
> The diff coverage is `33.33%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25573/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #25573       +/-   ##
===========================================
- Coverage   91.26%   41.71%   -49.55%     
===========================================
  Files         173      173               
  Lines       52966    52968        +2     
===========================================
- Hits        48337    22096    -26241     
- Misses       4629    30872    +26243
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `41.71% <33.33%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/json/json.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vanNvbi5weQ==) | `62.79% <33.33%> (-30.44%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY2F0ZWdvcmljYWwucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-99.36%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-95.46%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.17%)` | :arrow_down: |
| [pandas/io/sas/sas\_xport.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfeHBvcnQucHk=) | `0% <0%> (-90.15%)` | :arrow_down: |
| ... and [131 more](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=footer). Last update [3e652ac...e3bb759](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=h1) Report
> Merging [#25573](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3e652ac565e054b763ccbe23006c02704f6cd1b1?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `66.66%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25573/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25573      +/-   ##
==========================================
- Coverage   91.26%   91.25%   -0.01%     
==========================================
  Files         173      173              
  Lines       52966    52968       +2     
==========================================
+ Hits        48337    48338       +1     
- Misses       4629     4630       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.83% <66.66%> (-0.01%)` | :arrow_down: |
| #single | `41.71% <33.33%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/json/json.py](https://codecov.io/gh/pandas-dev/pandas/pull/25573/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vanNvbi5weQ==) | `93.02% <66.66%> (-0.21%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=footer). Last update [3e652ac...e3bb759](https://codecov.io/gh/pandas-dev/pandas/pull/25573?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
