Fix Travis CI cache

[Franz Josef Kaiser]

Type of issue: Bug report

Expected/Desired behavior

Travis CI should use the Bundler cache to fetch Gems from there to speed up the build. This should happen automatically.

Actual/Current behavior

Travis CI does not yet enable cache per default. Cache therefore fails miserably.

Proposed Change

The .travis.yml file in theory is set up properly. Practically, there's no boolean value, just a list of values for enabled caches, per the Travis docs:

language: ruby
cache:
  - bundler

It seems the boolean syntax is only used when disabling caches or when used in combination with directories directive:

cache:
  bundler: true
  directories:
  - vendor/something
  - .autoconf

cache:
  bundler: false
  apt: true

^ not sure why that should work.

[Franz Josef Kaiser]

The changes in 52da6a8 did not fix the build cache problem.