Use should pass instead of should_not fail_hook

Author: davidstosik

spec/overcommit/hook/pre_commit/file_size_spec.rb

@@ -40,7 +40,7 @@
   context 'when a small file is committed' do
     let(:contents) { 'short' }
 
-    it { should_not fail_hook }
+    it { should pass }
   end
 
   context 'when a file is removed' do