Error on byte compiler warnings on Travis CI

Our code must be free of warnings.
Update to recent Google This versions
Fix Rubocop tests
Call the autoloaded Google This function

Regression from 7dccd8a
Signal an error early when selecting an unusable checker
Fix nil handling in flycheck-select-checker
Add RPM Spec syntax checker [#480]
Remove --info from rpmlint checker

We don't parse the info messages anyway, so there's no use in emitting
them.
Simplify line number correction of rpmlint
Install rpmlint in the testing environments
Improve the rpmlint test case

Include an error, and messages with line numbers
Support RPM Spec Mode in rpm-rpmlint
Let users always disable Flycheck Mode in the menu
[Fix #481] Merge branch 'rpmlint'

* rpmlint:
  Support RPM Spec Mode in rpm-rpmlint
  Improve the rpmlint test case
  Install rpmlint in the testing environments
  Simplify line number correction of rpmlint
  Remove --info from rpmlint checker
  Add RPM Spec syntax checker [#480]
Update changelog, credits and texinfo manual [#481]
Remove unused extlink
Move the index before licensing
Directly include credits into front page
Restructure the credits

Make maintenance simpler, and reduce the text contents.  Also, separate
real code contributions from other contributions, and from unrelated
thanks
Remove unused document