Clear out lib/ directory when rebuilding

Author: dupski

package.json

@@ -4,7 +4,7 @@
   "main": "lib/index.js",
   "license": "MIT",
   "scripts": {
-    "build": "tslint -p . && tsc",
+    "build": "tslint -p . && rm -rf lib/ && tsc",
     "test": "mocha -r ts-node/register --recursive \"./src/**/__tests__/*\"",
     "test-watch": "mocha -r ts-node/register --recursive \"./src/**/__tests__/*\" --watch --watch-extensions ts,tsx",
     "prepublish": "npm run build && npm run test"