fix interpreting int as second--> nano
The existing behavior was put in place in #4684, looks like wrestling with numpy 1.6 and 1.7 was rough.

Not sure what this merits in the whatsnew, pls advise.

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Travis fail is hypothesis Closes #19233 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=h1) Report
> Merging [#24694](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/021cbae52061b660b2251d6c4dbbfa6d2a246325?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `0%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24694/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24694      +/-   ##
==========================================
+ Coverage   43.06%   43.06%   +<.01%     
==========================================
  Files         166      166              
  Lines       52310    52310              
==========================================
+ Hits        22526    22529       +3     
+ Misses      29784    29781       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #single | `43.06% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/24694/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `52.71% <0%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24694/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `50.73% <0%> (-0.93%)` | :arrow_down: |
| [pandas/io/json/json.py](https://codecov.io/gh/pandas-dev/pandas/pull/24694/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vanNvbi5weQ==) | `62.85% <0%> (+1.19%)` | :arrow_up: |
| [pandas/core/internals/construction.py](https://codecov.io/gh/pandas-dev/pandas/pull/24694/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2NvbnN0cnVjdGlvbi5weQ==) | `64.21% <0%> (+2.03%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24694?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/24694?src=pr&el=footer). Last update [021cbae...f059530](https://codecov.io/gh/pandas-dev/pandas/pull/24694?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/24694?src=pr&el=h1) Report
> Merging [#24694](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/021cbae52061b660b2251d6c4dbbfa6d2a246325?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24694/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24694      +/-   ##
==========================================
+ Coverage   92.38%   92.38%   +<.01%     
==========================================
  Files         166      166              
  Lines       52310    52311       +1     
==========================================
+ Hits        48327    48328       +1     
  Misses       3983     3983
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <100%> (ø)` | :arrow_up: |
| #single | `43.06% <0%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/24694/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `94.31% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24694?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/24694?src=pr&el=footer). Last update [021cbae...e9cb0ab](https://codecov.io/gh/pandas-dev/pandas/pull/24694?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Reverted change, made a deprecation instead. lgtm. ping on green.