Fix SpaceBeforeBrace bug for interpolations

This fixes an issue where `scss-lint` reported a lint for css statements
using interpolations in mixins such as:

    .#{$class}{ #{$property}: 10px;}

The solution was to add the hash to the preceding character exclusion.

Change-Id: I6554ec8804da6554e247f55d57ae8c3cfd8bdd52
Reviewed-on: http://gerrit.causes.com/36590
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>