fixes build:clean to keep dist folder

Author: vincentaudebert

package.json

@@ -14,7 +14,7 @@
     "js": "babel -d dist src",
     "js:watch": "npm run js -- --watch",
     "build:css": "cp src/css/*.css dist",
-    "build:clean": "rm -rf dist/",
+    "build:clean": "rm -rf dist/*",
     "build:rollup": "NODE_ENV=production rollup -c",
     "build:flow": "flow-copy-source src dist/es -i \"**/*.spec.js\"",
     "build": "npm run build:clean && npm run build:css && npm run build:flow && npm run build:rollup",