staticDir doesn't work if it ends with /
if staticDir is `/foo/bar/` and there's a file in `/foo/bar/baz.txt`, a request for `/baz.txt` won't succeed.
(it works if staticDir is `/foo/bar`)

either jester should call `doAssert staticDir == staticDir.normalizedPath` somewhere in the code (where all code paths lead to) or allow it, as done in https://github.com/dom96/jester/pull/197