Keep `compileSpec` name consistently.
Call parent classes constructor.

In the future `broccoli-filter` base class may have more functionality
added to its constructor. This keeps us as "future-proof" as possible.
Remove test dependence on specific compiler output.
Merge pull request #1 from rwjblue/small-rename

Keep `compileSpec` name consistently.
Merge pull request #2 from rwjblue/call-filters-super

Call parent classes constructor.
Merge pull request #3 from rwjblue/slight-refactor-tests

Remove test dependence on specific compiler output.
Default to HandleBars