Bump scss-tokenizer@^0.3.0

This requires dropping support Node < 6 due to a transitive
dependency.

https://github.com/mozilla/source-map/blob/master/CHANGELOG.md#070

Author: xzyfer

package.json

@@ -20,7 +20,7 @@
   "dependencies": {
     "glob": "^7.0.0",
     "lodash": "^4.0.0",
-    "scss-tokenizer": "^0.2.3",
+    "scss-tokenizer": "^0.3.0",
     "yargs": "^10.0.3"
   },
   "devDependencies": {