[ci] Don't fail on brew warnings

Not the best fix but it works and we don't care about brew warnings, so

.travis.yml

@@ -52,7 +52,7 @@ matrix:
         - brew update;
           # Workaround Travis/brew bug
         - brew uninstall libtool && brew install libtool
-        - brew install ragel freetype glib gobject-introspection cairo icu4c graphite2
+        - brew install ragel freetype glib gobject-introspection cairo icu4c graphite2 || true
         - brew link --force icu4c # icu4c is keg-only
       script:
         - ./autogen.sh