Add git to allow rake build

Author: mattes

Dockerfile

@@ -1,12 +1,12 @@
 FROM ubuntu:trusty
 
 RUN apt-get update
-RUN apt-get install -yq ruby ruby-dev build-essential
+RUN apt-get install -yq ruby ruby-dev build-essential git
 RUN gem install --no-ri --no-rdoc bundler
 ADD Gemfile /app/Gemfile
 ADD Gemfile.lock /app/Gemfile.lock
 RUN cd /app; bundle install
 ADD . /app
 EXPOSE 4567
 WORKDIR /app
-CMD ["bundle", "exec", "middleman", "server"]
+CMD ["bundle", "exec", "middleman", "server"]