enable caching for pull requests
Remove CouchDB hack

Build images should no longer start CouchDB on boot, so we remove this ugly hack.
Merge pull request #307 from travis-ci/ha-bug-remove-couchdb-hack

Remove CouchDB hack
Set TRAVIS_CMD when no script is given for Python

Fixes https://github.com/travis-ci/travis-ci/issues/2870

Without this, `$TRAVIS_CMD` is set to whatever was executed beforehand
(e.g., `install` or `before_install` command), which could very well
have succeeded, but the absence of `script` will display the confusing
message:

    The command "$TRAVIS_CMD" exited with 1.
Merge pull request #308 from travis-ci/ha-bug-python-no-script-message

Set TRAVIS_CMD when no script is given for Python
Bumping ruby version, only setting constraint on heroku

plus bumping travis-support dependency.
Provide built-in Godep support
Adjust the gopath bin to use a fully defined path
Merge pull request #309 from zackkitzmiller/master

Provide built-in Godep support
Minor touchup post-merge of #309
Only install Godeps/Godep requirements in go_version >= 1.1
Merge pull request #310 from zackkitzmiller/master

Only install Godeps/Godep requirements in go_version >= 1.1
Godep integration behavior updates per feedback from @kr on #309
Merge pull request #305 from travis-ci/rkh-cache-prs

enable caching for pull requests
Change firefox download location

releases.mozilla.org is CDN'd, while ftp.mozilla.org is not.
This should result in much faster downloads when the pre-installed
firefox is not sufficient.
Fix spec to match the previous commit
Merge pull request #312 from travis-ci/db-godep-tweaks

Godep integration behavior updates per feedback from @kr on #309
Exporting NVM_NODEJS_ORG_MIRROR to work around nodejs.org switch to https
Merge pull request #313 from travis-ci/db-bugfix-nvm-workaround

Exporting NVM_NODEJS_ORG_MIRROR to work around nodejs.org switch to https
Re-sourcing nvm.sh