net/url: fix stale RFC 3986 links
net/url: fix stale RFC 3986 links

The URLs for RFC 3986 have been changed from:
  http://tools.ietf.org/html/rfc3986
to:
  https://datatracker.ietf.org/doc/html/rfc3986

Change-Id: I0662557d91bbb7de51d7ca4bc64e838741cd9074
Reviewed-on: https://go-review.googlesource.com/c/go/+/356429
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Emmanuel Odeke <bd234ba4276433f0e5fc7a8fa2d18274fa711567@orijtech.com>
Trust: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

nawawi/go,nawawi/go,cloudflare/go,nawawi/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,golang/go,golang/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,CAFxX/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,golang/go,golang/go,CAFxX/go,cloudflare/go,golang/go