Fixup gemspec

There's important stuff in bin and config that should be packaged with
the gem.

Additionally, remove dependency on `git`, since I have no untracked
files in these directories.

Change-Id: I163725c7ce4057fd874e6d57c23be53ab1eab425
Reviewed-on: https://gerrit.causes.com/22750
Tested-by: Aiden Scandella <aiden@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>

Author: Aiden Scandella

overcommit.gemspec

@@ -17,5 +17,7 @@ Gem::Specification.new do |s|
 
   s.executables = ['overcommit']
 
-  s.files = `git ls-files -- lib`.split("\n")
+  s.files = Dir['lib/**/*.rb'] +
+            Dir['bin/**/*'] +
+            Dir['config/*.yml']
 end