Do not fail if git commit exits with non-zero, it means no changes

Author: eregon

build.rb

@@ -32,4 +32,4 @@ def sh(*command)
 File.write(file, lines.join)
 
 sh 'git', 'add', file
-sh 'git', 'commit', '-m', "Build #{versions.join(',')}"
+system 'git', 'commit', '-m', "Build #{versions.join(',')}"