Mechanism for forcing a golint update

They don't version releases, so it's always a matter of installing
whatever's latest. Similar to some other projects, I've added a file we
can touch to force expire docker layer caches & get a new version.

Author: wfleming

DATE_BUILT

@@ -0,0 +1 @@
+Tue Oct 17 12:36:42 EDT 2017

Dockerfile

@@ -4,6 +4,7 @@ MAINTAINER Code Climate <hello@codeclimate.com>
 
 WORKDIR /usr/src/app
 COPY codeclimate-golint.go /usr/src/app/codeclimate-golint.go
+COPY DATE_BUILT /usr/src/app/DATE_BUILT
 
 RUN apk --update add go git && \
   export GOPATH=/tmp/go GOBIN=/usr/local/bin && \

README.md

@@ -31,6 +31,12 @@ engines:
 docker build -t codeclimate/codeclimate-golint .
 ```
 
+### Updating
+
+`golint` doesn't version releases, so in order to get the latest version & force
+a new docker image build, we have a `DATE_BUILT` file: to force an update of
+golint, run `date > DATE_BUILT` locally & then rebuild the docker image.
+
 ### Need help?
 
 For help with Golint, [check out their documentation](https://github.com/golang/lint).