Go to cursor current line after starting timemachine

I have been using this functionality as an advice for some time.

Now when calling `git-timemachine` interactively, it will move to the line you had the cursor before calling `git-timemachine`.
You should use `(goto-char (point-min)) + (forward-line (1- cur-line))` instead of `goto-line`,
because `goto-line` causes byte-compile warning.