doc,n-api: update matrix for N-API version 4

The N-API version was bumped to 4 for Node.js 10 in
nodejs#25633

Refs: nodejs#25633

PR-URL: nodejs#27832
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

doc/api/n-api.md

@@ -150,7 +150,7 @@ available to the module code.
 | v6.x  |         |          | v6.14.2* |          |
 | v8.x  | v8.0.0* | v8.10.0* | v8.11.2  |          |
 | v9.x  | v9.0.0* | v9.3.0*  | v9.11.0* |          |
-| v10.x |         |          | v10.0.0  |          |
+| v10.x |         |          | v10.0.0  | REPLACEME |
 | v11.x |         |          | v11.0.0  | v11.8.0  |
 
 \* Indicates that the N-API version was released as experimental