doc: fix added: info for outgoingMessage.{,un}cork()

`outgoingMessage.cork()` and `outgoingMessage.uncork()` were added to
Node.js v13.2.0 via 62e15a7 and backported to Node.js v12.16.0 via
db8144b.

PR-URL: #42711
Reviewed-By: Paolo Insogna <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Akhil Marsonya <[email protected]>
Reviewed-By: Mestery <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: lpinca

doc/api/http.md

@@ -2491,7 +2491,9 @@ Aliases of `outgoingMessage.socket`
 ### `outgoingMessage.cork()`
 
 <!-- YAML
-added: v14.0.0
+added:
+  - v13.2.0
+  - v12.16.0
 -->
 
 See [`writable.cork()`][].
@@ -2697,7 +2699,9 @@ After calling `outgoingMessage.end()`, this property will be nulled.
 ### `outgoingMessage.uncork()`
 
 <!-- YAML
-added: v14.0.0
+added:
+  - v13.2.0
+  - v12.16.0
 -->
 
 See [`writable.uncork()`][]