DEPS: bump xlrd min version to 1.0.0
remove numpy warnings on np.diff in boolean arrays

removes all of those annoying warnings on 2.7 build :> # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23774?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@2946745`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23774/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23774?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #23774   +/-   ##
=========================================
  Coverage          ?   92.28%           
=========================================
  Files             ?      161           
  Lines             ?    51451           
  Branches          ?        0           
=========================================
  Hits              ?    47483           
  Misses            ?     3968           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <100%> (?)` | |
| #single | `42.28% <33.33%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23774?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/23774/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9wZXJpb2QucHk=) | `93.07% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23774?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/23774?src=pr&el=footer). Last update [2946745...b1cf09f](https://codecov.io/gh/pandas-dev/pandas/pull/23774?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @jreback! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/core/indexes/period.py`](https://github.com/jreback/pandas/blob/64d00972ad0d7bc27d16ab618f2fc60ce1ecfc5b/pandas/core/indexes/period.py) !

 @TomAugspurger if any comments