Fixing `cla` and `mod` snippets

The `cla` snippet would previously resolve to `class << self .. end` and
resolves now to `class .. end`.

The `mod` snippet would previously resolve to
`module .. module_function .. end` and resolves now to `module .. end`.
Merge pull request #38 from simonc/38-fix-cla-and-mod

The cla prefix is used for class << self instead of class