postinstall 加编译判断

package.json

@@ -2,10 +2,9 @@
   "name": "amap-shapes-generator",
   "version": "0.0.1",
   "private": true,
-  "main": "./lib/index.js",
   "scripts": {
     "build": "babel *.js --presets babel-preset-es2015 -d lib",
-    "postinstall": "../../node_modules/.bin/babel *.js --presets babel-preset-es2015 -d lib",
+    "postinstall": "[ -f ../../node_modules/.bin/babel ] && ../../node_modules/.bin/babel *.js --presets babel-preset-es2015 -d lib",
     "test": "jest"
   },
   "dependencies": {