Send invite email in the server console in development mode

Meteor support that use case for us, we don't need to implement our
own validate strategy on top of that. This was also discussed as part
of the #454 review.

models/users.js

@@ -166,12 +166,9 @@ if (Meteor.isServer) {
       board.addMember(user._id);
       user.addInvite(boardId);
 
-      if (!process.env.MAIL_URL || (!Email)) return { username: user.username };
-
       try {
-        let rootUrl = Meteor.absoluteUrl.defaultOptions.rootUrl || '';
-        if (!rootUrl.endsWith('/')) rootUrl = `${rootUrl}/`;
-        const boardUrl = `${rootUrl}b/${board._id}/${board.slug}`;
+        const { _id, slug } = board;
+        const boardUrl = FlowRouter.url('board', { id: _id, slug });
 
         const vars = {
           user: user.username,