Although we thought the upgrade from `npm` 3.10.9 to 4.1.2 was worthwhile
and safe, this breaking change proved problematic:
https://github.com/npm/npm/blob/latest/CHANGELOG.md#no-more-partial-shrinkwraps-breaking

Specifically, if a Meteor package calls `Npm.depends` in a way that
disagrees with the contents of `.npm/package/npm-shrinkwrap.json` file,
Meteor will create a partial shrinkwrap file in order to install the
correct top-level npm dependencies, but transitive dependencies of the
package will no longer be installed.

This was fixed in Meteor 1.4.2.7 by reverting the upgrade of npm, but
Meteor 1.4.3.1 will keep npm@4.1.2 and fix the consequences.

Thanks to @abernix for fixing this Babel/Babylon bug in Reify:
benjamn/reify#62

Fixes #8312.

@abernix Bumping the ecmascript version is apparently necessary if the
babel-compiler package has changed, presumably because ecmascript defines
a compiler plugin that uses babel-compiler. Unless the ecmascript version
has been bumped, babel-compiler changes won't appear to have any effect.