TST: Check pytables<3.5.1 when skipping
`3.5.1` was made available on `conda`, causing `xfail_non_writeable` tests to fail.

Note that this is just to get `master` to pass again (started failing when #25751 was merged).

This new release of `pytables`, however, brings up the question of how we want to proceed with #24839, as it appears that all of our CI builds that install `pytables` will use this version now.

It seems a little early to declare that `3.5.1` is our minimum version, but it definitely looks like we *could* drop this `xfail` from our tests at some point in the near future.
Really strange `geopandas` failure [here](https://travis-ci.org/pandas-dev/pandas/jobs/508237658#L2313).  Doesn't seem related to my PR though...

I also see no changes in the `geopandas` and `fiona` versions.  Any ideas? > Any ideas?

@gfyoung : there was a `ResourceWarning: unclosed <ssl.SSLSocket [closed] fd=180, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6>` ealier in the logs. could this have messed things up. maybe worth restarting the job.

 > Really strange geopandas failure here. Doesn't seem related to my PR though...

That's indeed not related. It is a failure with one of the dependencies. It might well be it is only temporary (eg when they are updating packages on conda-forge, there might be a moment not yet everything is matching with each other). But if it keeps failing, we can skip it for now. > But if it keeps failing, we can skip it for now.

@jorisvandenbossche : Sounds good.  I'll restart again tomorrow. Just restarted the build now @gfyoung you can just put a skip around geopandas for now (or pin to a prior version) @jreback see https://github.com/pandas-dev/pandas/issues/25778 for the geopandas issue. Skipping here is fine, I can fix it later in a separate PR. we shouldn't block on installation issues of another library here. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25773?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@c8ba766`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25773/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25773?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #25773   +/-   ##
=========================================
  Coverage          ?   41.76%           
=========================================
  Files             ?      172           
  Lines             ?    52965           
  Branches          ?        0           
=========================================
  Hits              ?    22122           
  Misses            ?    30843           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #single | `41.76% <ø> (?)` | |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25773?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/25773?src=pr&el=footer). Last update [c8ba766...9d61a0b](https://codecov.io/gh/pandas-dev/pandas/pull/25773?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/25773?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@c8ba766`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25773/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25773?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #25773   +/-   ##
=========================================
  Coverage          ?   91.26%           
=========================================
  Files             ?      172           
  Lines             ?    52965           
  Branches          ?        0           
=========================================
  Hits              ?    48338           
  Misses            ?     4627           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.82% <ø> (?)` | |
| #single | `41.74% <ø> (?)` | |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25773?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/25773?src=pr&el=footer). Last update [c8ba766...9d61a0b](https://codecov.io/gh/pandas-dev/pandas/pull/25773?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. ping on green. thanks @gfyoung 