syntax: add vaderComment to contains for blocks

I've tried to come up with a test for this, but failed at providing the to-be-tested vader script in a "Given" block.

This is where I stopped:


    % cat test/feature/syntax.vader
    Given vader (Vader file):
    Do():
    " comment
      echom "Command"

    Execute():
      AssertEqual "vaderComment VaderDo", SyntaxAt(2,1)
      AssertEqual "vaderCommand", SyntaxAt(4,3)