Log Message:
Update tex-fontspec{,-doc} to 2.6c

- v2.6b (2017/07/16)

    * Fix conflict with Polyglossia and `Scale=MatchLowercase`.
    * New feature `IgnoreFontspecFile` to avoid loading the `.fontspec`
      file for a font.
    * Fix regression with `\fontspec_if_feature:nTF`
      (which broke `realscripts`, oops — must improve my test suite)