make test: Fix mocha timeout @ 'Plural Forms Parsing should have the sam...

Hey,

With this fix `make test` is error free!  My Mac needs 6 seconds with the current HEAD, Travis CI needs 3 seconds.  This patched version is a bit less than 1 second on my Mac, so it should be half a second on Travis CI which is way less than mocha's default timeout of 2 seconds...

expect.js's `be` and `to` functions aren't really complex but heavy enough to be more than 6x slower than a simple `!==` + `throw`.

Cheers, Philip