Ignore directories when recursively scanning
Ignore directories when recursively scanning

The call to `Find.find` was already recursing, but it was adding
directory names onto the `files` list, which in turn was causing the
Sass engine to choke trying to load a directory as a file.

Fixes #4.

Change-Id: I7c59ea3ff08410602d9e85459d8d615b49be9cb0
Reviewed-on: https://gerrit.causes.com/19252
Tested-by: jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@causes.com>
Reviewed-by: Greg Hurrell <79e2475f81a6317276bf7cbb3958b20d289b78df@causes.com>

philipgiuliani/scss-lint,teoljungberg/scss-lint,golmansax/scss-lint,baileyparker/scss-lint,leseulsteve/scss-lint,cih/scss-lint,ivantsepp/scss-lint,ingdir/scss-lint,gatero/scss-lint,gajus/scss-lint,dwayhs/scss-lint,bkeepers/scss-lint,chatzipan/scss-lint,davecarter/scss-lint