feat(godeps): speed up `git push` by specifying go dependencies

I added a `Godeps` folder into the project to speed up buildpack compiles, according to [these instructions](https://github.com/tools/godep#install). The app is now somewhat faster to deploy as it doesn't bother to set up `hg` or `bzr`:
```console
gradishar:example-go matt$ git push deis master
Counting objects: 8, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (5/5), done.
Writing objects: 100% (7/7), 684 bytes | 0 bytes/s, done.
Total 7 (delta 1), reused 0 (delta 0)
-----> Go app detected
-----> Installing go1.2.2... done
-----> Running: godep go install -tags heroku ./...
-----> Discovering process types
       Procfile declares types -> web
-----> Compiled slug size is 1.7M
remote: -----> Building Docker image
remote: Uploading context 1.796 MB
remote: Uploading context 
remote: Step 0 : FROM deis/slugrunner
remote:  ---> 683f264537a0
remote: Step 1 : RUN mkdir -p /app
remote:  ---> Using cache
remote:  ---> 42808a9f386d
remote: Step 2 : ADD slug.tgz /app
remote:  ---> b7c5a5e3aa2b
remote: Removing intermediate container fbc689e36ac0
remote: Step 3 : ENTRYPOINT ["/runner/init"]
remote:  ---> Running in f27c7a6b55a7
remote:  ---> c29b275316c4
remote: Removing intermediate container f27c7a6b55a7
remote: Successfully built c29b275316c4
remote: -----> Pushing image to private registry
remote: 
remote:        Launching... done, v3
remote: 
remote: -----> folksy-greenery deployed to Deis
remote:        http://folksy-greenery.local3.deisapp.com
remote: 
remote:        To learn more, use `deis help` or visit http://deis.io
remote: 
To ssh://git@deis.local.deisapp.com:2222/folksy-greenery.git
   459598b..4de6744  master -> master
```