Group Gemfile orders in Dockerfile together

The blank line between each order made it harder to read this file, and
we can use a shortcut to include all gemfiles.

Dockerfile

@@ -28,11 +28,7 @@ WORKDIR $RAILS_ROOT
 # Use the Gemfiles as Docker cache markers. Always bundle before copying app src.
 # (the src likely changed and we don't want to invalidate Docker's cache too early)
 # http://ilikestuffblog.com/2014/01/06/how-to-skip-bundle-install-when-deploying-a-rails-app-to-docker/
-COPY Gemfile Gemfile
-
-COPY Gemfile.lock Gemfile.lock
-
-COPY Gemfile_custom Gemfile_custom
+COPY Gemfile* ./
 
 # Finish establishing our Ruby environment
 RUN bundle install --full-index