gem update --system 2.2.3 on travis-ci

Author: kares

.travis.yml

@@ -33,6 +33,8 @@ before_script:
   - export JRUBY_OPTS="--server -Xcext.enabled=false -Xcompile.invokedynamic=false -J-XX:MaxPermSize=128m"
   - export JRUBY_VERSION="1.7.12"
 before_install:
+  # NOTE: RubyGems 2.4.x fails us at application_spec's gem_install_rack_unless_installed !
+  - (jruby --1.9 -S gem update --system 2.2.3) || true
   - ((jruby -v | grep 1.8.7) && jruby --1.9 -S gem update --system 2.1.11) || true
   - ((echo $BUNDLE_GEMFILE | grep rails23) && jruby --1.9 -S gem update --system 1.8.29) || true
 matrix: