Ensure timestamp always properly converted to int

In windows, `git log -1 --pretty=format:'%ct'` would sometimes return
the timestamp surrounded by quotes, so it wouldn't be properly converted
to an integer. The new command seems to work in all cases.

Author: David Rodríguez de Dios

lib/code_climate/test_reporter/git.rb

@@ -32,7 +32,7 @@ def clean_git_branch
         private
 
         def committed_at
-          committed_at = `git log -1 --pretty=format:'%ct'`
+          committed_at = `git log -1 --pretty=format:%ct`
           committed_at.to_i.zero? ? nil : committed_at.to_i
         end
 

spec/lib/git_spec.rb

@@ -6,7 +6,7 @@ module CodeClimate::TestReporter
       it 'returns a hash with git information.' do
         expected_git_hash = {
           head: `git log -1 --pretty=format:'%H'`,
-          committed_at: `git log -1 --pretty=format:'%ct'`.to_i,
+          committed_at: `git log -1 --pretty=format:%ct`.to_i,
           branch: Git.send(:branch_from_git)
         }