Update yargs to v4.7.1 from v3.32.0

Author: watilde

index.js

@@ -44,7 +44,7 @@ var argv = require("yargs")
       'postcss version',
       require('./node_modules/postcss/package.json').version
     ].join(' ');
-  }, 'v')
+  })
   .alias('v', 'version')
   .help('h')
   .alias('h', 'help')

package.json

@@ -24,7 +24,7 @@
     "postcss": "^5.0.0",
     "read-file-stdin": "^0.2.0",
     "resolve": "^1.1.6",
-    "yargs": "^3.32.0"
+    "yargs": "^4.7.1"
   },
   "optionalDependencies": {
     "chokidar": "^1.0.3"