Quick release for a bug that slipped in the 2.1.3 release in the r.js optimizer. So even though require.js now has a 2.1.4 version, it is the same as 2.1.3, and the optimizer is the same as 2.1.3 except for this one fix:
Without this fix, in some cases 2.1.3 would insert "undefined" in some optimized CSS files, making them unusable.