ensure that new user's `isGravatarEnabled` attribute is set to false

lib/models/user.js

@@ -658,7 +658,7 @@ module.exports = function(crowi) {
     newUser.email = email;
     newUser.setPassword(password);
     newUser.lang = lang;
-    newUser.isGravatarEnabled = true;   // Gravatar enabled in default
+    newUser.isGravatarEnabled = false;
     newUser.createdAt = Date.now();
     newUser.status = decideUserStatusOnRegistration();