crypto/tls: ambiguous comment in cipher_suites.go

[d1str0]

https://github.com/golang/go/blob/master/src/crypto/tls/cipher_suites.go#L77

This line says "RC4 comes before AES (because of the Lucky13 attack)" when it should be clarified that AES-GCM is safe and therefore preferred over RC4.

[d1str0]

https://go-review.googlesource.com/#/c/19845/