Correct assignment for assert.notInclude() synonym assert.notIncludes()

In reviewing the diffs from 0.7.0 to 0.8.0 I saw that the synonym
"notIncludes" had been added and was assigned to itself (which makes
it undefined).

This patch adds a unit test to make sure that the notIncludes synonym
exists and works correctly, and fixes the assignment.
Merge pull request #319 from evanp/assert-not-includes

Correct assignment for assert.notInclude() synonym assert.notIncludes()