Fix booleans in config file

Due to yargs/yargs#223, using booleans in the
config file doesn't work if `npm install` picks up a version of yargs
lower than 3.18.1, so bump yargs to 3.32.0

package.json

@@ -23,7 +23,7 @@
     "postcss": "^5.0.0",
     "read-file-stdin": "^0.2.0",
     "resolve": "^1.1.6",
-    "yargs": "^3.8.0"
+    "yargs": "^3.32.0"
   },
   "optionalDependencies": {
     "chokidar": "^1.0.3"