Stop packaging test files with the gem

See [this issue on the Bundler repository][issue3207] for reasoning.

Basically the test files are available on at the gem's site (Github) and
aren't needed for executing the code. If you want to hack on the gem,
get it with git.

[issue3207]: rubygems/bundler#3207

omniauth-eventbrite.gemspec

@@ -13,7 +13,6 @@ Gem::Specification.new do |spec|
   spec.description = spec.summary
 
   spec.files         = `git ls-files`.split("\n")
-  spec.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
   spec.require_paths = ['lib']
 
   spec.add_dependency 'omniauth-oauth2', '~> 1.0'