修复 postinstall

package.json

@@ -4,7 +4,7 @@
   "private": true,
   "scripts": {
     "build": "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",
+    "postinstall": "[ -f ../../node_modules/.bin/babel ] && ../../node_modules/.bin/babel *.js --presets babel-preset-es2015 -d lib || echo 'no babel found, skip build'",
     "test": "jest"
   },
   "dependencies": {