Update local ERFA to include 2015-Jun-30 leap second - #3794

@taldcroft - looks good, like the updated test. I restarted the one travis job that failed (seemed to have timed out on something).

It looks like the appveyor build is stuck permanently. Can anyone restart this?

@taldcroft -- several days of astropy appveyor tests are stalled....contacting appveyor support.

cc @astrofrog

Should we be making a release once this is merged?

Changelog nag (this seems like an important one too)

@embray - yes, a release would be good.

From @sergiopasra :

For package managers that use a system-installed erfa, we need a new release of the library
liberfa/erfa#28

It seems maybe we have a problem here with the (quick) local patch. The issue is that I don't know for sure if ERFA 1.2 is strictly back-compatible and qualifies as a bug fix. Then there is the organizational issue of getting out the release.

@taldcroft - I'm almost sure 1.2 is backwards-compatible. (Technically it isn't "1.2" if it isn't, anyway...) Will try to get a release out ASAP, and then that can be incorporated into astropy for sanity's sake.

Well, who's determining the version numbers for ERFA? Are they just mirroring the SOFA versions? In that case there's no guarantee they're using anything resembling semantic versioning :)

@embray - we are: see https://github.com/liberfa/erfa/blob/master/RELEASE.rst#version-numbering where this is all laid out. the SOFA scheme really makes no sense in this regard so we're keeping strictly to semantic + the standard unix-y shared library scheme.

@taldcroft - see #3802, which updates to the just-release 1.2.0 . That should make everything happy again.