fix compile error

git.go

@@ -73,7 +73,7 @@ func init() {
 func Fsck(repoPath string, timeout time.Duration, args ...string) error {
 	// Make sure timeout makes sense.
 	if timeout <= 0 {
-		timeout == -1
+		timeout = -1
 	}
 	_, err := NewCommand("fsck").AddArguments(args...).RunInDirTimeout(timeout, repoPath)
 	return err