Undo removal of libgirepository1.0-dev from Travis CI configuration.
Undo removal of libgirepository1.0-dev from Travis CI configuration.

This package is used in building the Regress and GIMarshallingTests test
libraries.

jcupitt/gir_ffi,jcupitt/gir_ffi,mvz/gir_ffi,mvz/gir_ffi,mvz/gir_ffi