Fixes _spacing typo

You were missing an "x" in your "mvxxl".
Merge branch 'davidpots-patch-1'

* davidpots-patch-1:
  Fixes _spacing typo
Updating gulpfile with more better workflow.

* Update skin classes for grays to be more verbose
* Update package.json with new devDependencies.
Merge branch 'master' into gh-pages

* master:
  Updating gulpfile with more better workflow.
  Fixes _spacing typo