Wrong behavoir of serve_static on Windows

[Sunrise]

On Windows, when serve_static is set true, behaviors to request for local resources will lead to a series of errors, including 304 resp status to a request for static files, none response for requests to obtain data from database etc.

grip/src/grip/handlers/static.cr

Line 29 in be4ac9f

 expanded_path = File.expand_path(request_path, "/") 

File.expand_path("/whois", "/") => C:\whois
This may be part of the cause of the problem.

[Sunrise]

A quick fix 6af00fa

[Giorgi Kavrelishvili]

Thank you for this fix!