Dockerfile: set WORKDIR to /code

This is best practice for engines now.

Author: Will Fleming

Dockerfile

@@ -17,4 +17,7 @@ USER app
 RUN cd /usr/src/app && \
     rake docs:scrape
 
+VOLUME /code
+WORKDIR /code
+
 CMD ["/usr/src/app/bin/codeclimate-rubocop"]

bin/codeclimate-rubocop

@@ -11,4 +11,4 @@ else
   engine_config = {}
 end
 
-CC::Engine::Rubocop.new("/code", engine_config, STDOUT).run
+CC::Engine::Rubocop.new(Dir.pwd, engine_config, STDOUT).run