update cextern/erfa to 1.1.0

[eteq]

This updates the copy of ERFA to the just-released v1.1.0

This closes #1031 because it was fixed in the latest SOFA release.

[astrofrog]

Should astropy include a regression test for #1031?

cc @taldcroft

[eteq]

Oh, that's a good idea - @taldcroft, feel free to either PR against my branch of this to add said test, or as a separate PR after this is merged.

[taldcroft]

Let's just go ahead and merge this and I'll write the regression test for #1031 after that.

[taldcroft]

Why aren't there any Travis results or tests pending? I would like to see that before merge!

[astrofrog]

Not sure why it didn't test the latest commit, but 41fc760
/ https://travis-ci.org/astropy/astropy/builds/25280521 passed, so good to go?

[eteq]

@taldcroft @astrofrog - There's no travis result shown on the merge button because 433f006 is the latest commit, and it has [ci skip] in the commit log (it's only the changelog entry and I didn't want to block up travis). But apparently that hides the merge status. As @astrofrog said, though, 41fc760 passed without problems, so I'll go ahead and merge this.