doc: tls.markdown, adjust version from v0.10.39 to v0.10.x

per https://github.com/joyent/node/pull/25591#discussion_r34824389

Reviewed-By: James M Snell <jasnell@gmail.com>
PR-URL: https://github.com/joyent/node/pull/25591

doc/api/tls.markdown

@@ -696,7 +696,7 @@ the total bytes written to the socket, *including the TLS overhead*.
 
 ## Class: CleartextStream
 
-The CleartextStream class in Node.js version v0.10.39 and prior has been
+The CleartextStream class in Node.js version v0.10.x (and prior) has been
 deprecated and removed.
 
 ## Class: tls.TLSSocket