crypto/tls: fix a typo

Change-Id: Id0044c45c23c12ee0bca362a9cdd25369ed7776c
Reviewed-on: https://go-review.googlesource.com/34533
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

conn.go

@@ -37,7 +37,7 @@ type Conn struct {
 	vers          uint16  // TLS version
 	haveVers      bool    // version has been negotiated
 	config        *Config // configuration passed to constructor
-	// handshakeComplete is true if the connection is currently transfering
+	// handshakeComplete is true if the connection is currently transferring
 	// application data (i.e. is not currently processing a handshake).
 	handshakeComplete bool
 	// handshakes counts the number of handshakes performed on the