follow-up to bf34a4cbed, which changed the
isWindowsDrivePath function to use a regex for matching the trailing slash.
This reverts it back to te previous implementation to avoid a regex, but
adds a check for the colon to be followed by a forward-slash, which is
faster, and avoids the overhead of `regex.MustCompile` during init.
BenchmarkRegex-11 39056917 32.45 ns/op 0 B/op 0 allocs/op
BenchmarkManual-11 1000000000 0.2476 ns/op 0 B/op 0 allocs/op
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>