Valid scheme produces Validation Error

e.g. 
ssh+git@github.com:kvesteri/validators.git#egg=validators
mailto:example@example.com

See also:
- https://tools.ietf.org/html/rfc3986.html#section-3.1
- https://tools.ietf.org/html/rfc3986.html#section-1.1.2
- https://tools.ietf.org/html/rfc2368.html