Fixes namespace issue

Hey,

first off, thanks for writing this awesome gem! While fiddling around with it I came about a minor issue: Grammar would not work for configuration due to a wrong namespace. This wasn't caught by tests since there the whole Pocketsphinx Namespace is loaded into the global namespace. I changed that and fixed the namespace issue in configuration/grammar.

* removed `include Pocketsphinx` statement from RSpec configuration since this hides any potential namespace issues from the test suite
* fixed namespace issue in `lib/pocketsphinx/configuration/grammar.rb` where wrong global-scope was used.