crypto/tls: fix typo in Config.NextProtos docs

Change-Id: I916df584859595067e5e86c35607869397dbbd8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/325651
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

src/crypto/tls/common.go

@@ -619,7 +619,7 @@ type Config struct {
  // protocol will be one from this list, and the connection will fail
  // if there is no mutually supported protocol. If NextProtos is empty
  // or the peer doesn't support ALPN, the connection will succeed and
- // ConnectionState.NegotiatedProtocol will be empty."
+ // ConnectionState.NegotiatedProtocol will be empty.
  NextProtos []string
 
  // ServerName is used to verify the hostname on the returned