update build script

Author: leaves4j

package.json

@@ -9,7 +9,7 @@
   "scripts": {
     "pretest": "npm run build",
     "check": "flow check",
-    "build:client":"babel src/plugins/client.js --out-file lib/plugins/client.js --presets=es2015 --plugins=transform-object-assign && cp lib/plugins/client.js dist/plugin.js",
+    "build:client":"babel src/plugins/client.js --out-file lib/plugins/client.js --presets=es2015 --plugins=transform-object-assign && mkdir dist; cp lib/plugins/client.js dist/plugin.js",
     "build:server": "npm run check && rm -rf lib/* && flow-remove-types src/ -d lib/ --pretty && rm -f lib/type.js",
     "build":"npm run build:client & npm run build:server",
     "test": "nyc ava",