Added other types to diff.test.js
Added other types to diff.test.js

Tests for bignumber, fraction and units.

josdejong/mathjs,FSMaxB/mathjs,josdejong/mathjs,FSMaxB/mathjs,josdejong/mathjs,josdejong/mathjs,FSMaxB/mathjs,FSMaxB/mathjs,FSMaxB/mathjs,josdejong/mathjs