Fix PropertySpelling treatment of nested properties

This linter would incorrectly report the following as a lint:

    p {
      text: {
        transform: uppercase;
      }
    }

Fix it to handle nested properties.

Change-Id: Ie3b4921713361d1af7b0b312309a8ebc0288762d
Reviewed-on: http://gerrit.causes.com/44136
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>