Incorrect result returned by is_valid_uri() #30

According to RFC 3986, there are some ABNF rules:

URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / ".")

And I tried:

>>> from rfc3986 import is_valid_uri
>>> is_valid_uri("1")
True
>>> is_valid_uri("//")
True
>>> is_valid_uri("http#:/")
True

I think these results are not correct.