Bump yargs@^13.3.2

Fixes #108

Author: xzyfer

package.json

@@ -21,7 +21,7 @@
     "glob": "^7.0.0",
     "lodash": "^4.17.11",
     "scss-tokenizer": "^0.3.0",
-    "yargs": "^12.0.2"
+    "yargs": "^13.3.2"
   },
   "devDependencies": {
     "assert": "^1.3.0",