Bundle test gems so this image can also be used for CI testing

Author: dhh

railties/lib/rails/generators/rails/app/templates/Dockerfile.tt

@@ -27,7 +27,7 @@ WORKDIR /rails
 ENV RAILS_LOG_TO_STDOUT="1" \
     RAILS_SERVE_STATIC_FILES="true" \
     RAILS_ENV="production" \
-    BUNDLE_WITHOUT="development:test"
+    BUNDLE_WITHOUT="development"
 
 # Install application gems
 COPY Gemfile Gemfile.lock ./