Update to Gradle 2.0

http://www.gradle.org/docs/current/release-notes
Use mongodb.org server to pull down packages

As a side effect, the installed version is now the latest
(which is 2.6.3 as of this commit) and this commit therefore
fixes https://github.com/travis-ci/travis-ci/issues/2246.
Default to Leiningen 2.x
Remove workaround for Leiningen 2.0 preview1
Update Haskell components

Fixes https://github.com/travis-ci/travis-ci/issues/2690.
Update ElasticSearch to 1.3.2
Merge pull request #350 from travis-ci/ha-feature-mongodb

Use mongodb.org server to pull down packages
Merge branch 'master' of github.com:travis-ci/travis-cookbooks
Merge pull request #361 from travis-ci/ha-feature-leiningen-2-default

Default to Leiningen 2.x
Update to Gradle 2.0

http://www.gradle.org/docs/current/release-notes
Merge pull request #343 from rtyley/gradle-2.0

Update to Gradle 2.0
Credit Roberto Tyley for Gradle 2.0 update
Merge remote-tracking branch 'origin/ha-feature-gradle-2.0'