Travis: Do not install GObject libraries
Currently linking `libelektra-io-glib` fails on macOS. The build system
reports the following error
> ld: library not found for -lintl
.
@@ -106,7 +106,6 @@ before_install:
brew install checkbashisms
brew install dbus
brew install discount
- brew install gobject-introspection
brew install libgcrypt
brew install libgit2
brew install libuv
