Update gitbook to 0.4.2

Author: SamyPesse

package.json

@@ -11,7 +11,7 @@
     "dependencies": {},
     "devDependencies": {
         "grunt": "~0.4.1",
-        "grunt-gitbook": "0.3.2",
+        "grunt-gitbook": "0.4.2",
         "grunt-gh-pages": "0.9.1",
         "grunt-contrib-clean": "~0.5.0",
         "grunt-http-server": "0.0.4"