docs: add ciphers option to https.request()

doc/api/https.markdown

@@ -94,6 +94,9 @@ specified. However, a [globalAgent](#https.globalAgent) silently ignores these.
 - `cert`: Public x509 certificate to use. Default `null`.
 - `ca`: An authority certificate or array of authority certificates to check
   the remote host against.
+- `ciphers`: A string describing the ciphers to use or exclude. Consult
+  <http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT> for
+  details on the format.
 - `rejectUnauthorized`: If `true`, the server certificate is verified against
   the list of supplied CAs. An `'error'` event is emitted if verification
   fails. Verification happens at the connection level, *before* the HTTP