Properly check to see if changes were made on push

The original implementation made poor assumptions about the name of the
pod, and used it as a regex pattern. This led to problems when trying to
push specs that contained special characters in their names (such as `+`
for category specs). Instead of using a regex, we should just do a
substring match to see if the output contains the spec name.

lib/cocoapods/command/push.rb

@@ -138,7 +138,7 @@ module Pod
           FileUtils.cp(spec_file, output_path)
           Dir.chdir(repo_dir) do
             # only commit if modified
-            if git!("status --porcelain 2>&1") =~ /#{spec.name}/
+            if git!("status --porcelain 2>&1").include? spec.name
               UI.puts " - #{message}"
               git!("add #{spec.name}")
               git!("commit --no-verify -m '#{message}'")