Remove all occurrences of the pace-running class instead of only one.

In the website where I used Pace, the `pace-running` class was being added multiple times on every page load. This made the element accumulate lots of `pace-running` classes, since according to the code, only one is removed.

Just like in code that removes the `pace-done` class, I added the same regexp to replace all occurrences of the `pace-running` class to avoid this behaviour.