Call configlet subcommand on CI (exercism#133)

This changes configlet to pass a subcommand.

For now, we've released a version of configlet which handles both the old command:

    configlet path/to/track

as well as the new command:

    configlet lint path/to/track

This will let us update all the travis files to include the subcommand before we
release the version of configlet that requires the subcommand.

.travis.yml

@@ -14,6 +14,6 @@ install:
 - sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 90
 script:
 - bin/fetch-configlet
-- bin/configlet .
+- bin/configlet lint .
 - cmake -G "Unix Makefiles"
 - make