BugFix use graceful-fs instead od hexo-fs

package.json

@@ -58,6 +58,7 @@
     "express-form": "~0.12.0",
     "express-session": "~1.14.0",
     "googleapis": "=12.3.0",
+    "graceful-fs": "^4.1.11",
     "gulp": "~3.9.0",
     "gulp-concat": "~2.6.0",
     "gulp-cssmin": "~0.1.7",
@@ -67,7 +68,6 @@
     "gulp-spawn-mocha": "~2.2.1",
     "gulp-uglify": "~1.4.2",
     "gulp-watch": "~4.3.5",
-    "hexo-fs": "^0.1.6",
     "highlight.js": "~9.9.0",
     "i18next": "~4.1.0",
     "i18next-express-middleware": "~1.0.2",