Change object construction to prevent Chrome v32 crashing.

Suspected JS execution optimizations in v32 is causing the browser to
throw "Aw, Snap".

See https://github.com/moment/moment/issues/1423
Merge pull request #1429 from thebestday/bugfix/chrome-v32

Change object construction to prevent Chrome v32 crashing.

@changelog
@section bugfix
Bump version to 2.5.1