This puts Meteor back on the official release track of Node.js 4, rather
than using its own custom build (from https://github.com/meteor/node/),
which had previously been necessary to add the garbage collection fixes
gained with
nodejs/node@751f1ac
and
nodejs/node@71f9cdf,
both of which are now officially included in Node.js 4.x as of 4.8.6.
:tada:

Alternatively, this was just failing when trying to download a file that
was 404-ing.  This just short-circuits before that inevitable failure.