[test] Fix shell not found error

[tay]

When I run git commit in my iTerm, I get the following error message from the precommit hook:

> memcached@0.2.8 test /Users/Fiona/workspace/node-memcached
> mocha $(shell find test -name '*.test.js')

sh: shell: command not found

This PRs uses a regexp to find the test files instead of calling out to shell find.

[3rd-Eden]

Thanks for your commit, i made small adjustment to your patch, I wanted to leave the find intact. Tests should still be working as intended now.

[tay]

Thanks for the quick turnaround!