use `shx` to execute cross-platform shell commands such as `rm -fr` & `cp`

package.json

@@ -16,9 +16,9 @@
   },
   "scripts": {
     "ts-node": "ts-node",
-    "build": "tsc && cp package.json dist/ && cp src/puppet-web/*.js dist/src/puppet-web/",
+    "build": "tsc && shx cp package.json dist/ && shx cp src/puppet-web/*.js dist/src/puppet-web/",
     "doctor": "ts-node bin/doctor",
-    "clean": "rm -fr dist/*",
+    "clean": "shx rm -fr dist/*",
     "lint": "npm run eslint && npm run tslint",
     "eslint": "eslint \"{bin,example,src,test}/**/*.js\"",
     "tslint": "tslint \"{bin,example,src,test}/**/*.ts\" && tsc --noEmit",
@@ -117,6 +117,7 @@
     "eslint": "^3.4.0",
     "eslint-plugin-ava": "^3.0.0",
     "qrcode-terminal": "^0.10.0",
+    "shx": "^0.1.4",
     "sinon": "^1.17.5",
     "sloc": "^0.1.11",
     "ts-node": "^1.4.1",