Allow rule sets to be followed by comments

Now that `scss-lint` supports control comments to enable/disable
linters, it is likely for rule sets to be preceded and followed by
comments enabling/disabling certain lints.

The `EmptyLineBetweenBlocks` linter would incorrectly report lints for
control comments following a rule set. Fix that by adjusting a regex.

Change-Id: I39f33b0290d5cf9ab2201b97c192e80d69c2a498
Reviewed-on: http://gerrit.causes.com/45100
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>