Update normalize_path like Rails

[ericproulx]

This PR apply the same strategy as Rails when normalizing path.

[grape-bot]

	1 Warning
⚠️	There're library changes, but not tests. That's OK as long as you're refactoring existing code.

Generated by 🚫 Danger

[dblock]

In what situations does this change behavior? There's a lot more going on here than in the Rails commit :) At the very least I feel like we need to bring in some tests from Rails for normalize_path if we're going to be doing it here as well.

[ericproulx]

@dblock I've added some specs. Basically, it does exactly the same thing but there's a faster path for the usual cases.