Set PHPUnit directory spec to only match project source.

This was done so that when generating a coverage report, it doesn't
count the vendor directory.
Use the NumberGenerator for getArrayValue.

This class can be used as a random number generator in other libraries
in order to provide the ability to mock the generator for tests.  Except
that this one method didn't use the number generator and therefore
wasn't affected by a mock number generator.
Merge pull request #1 from nubs/master

Use the NumberGenerator for getArrayValue