doc: added version 7 to N-API version matrix

Node.js version 14.12.0 released the N-API version 7, but it's not
present on the N-API version matrix. This change  should fix the problem
in the documentation.

PR-URL: #35319
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: NickNaso

doc/api/n-api.md

@@ -256,6 +256,7 @@ listed as supporting a later version.
     <th scope="col">4</th>
     <th scope="col">5</th>
     <th scope="col">6</th>
+    <th scope="col">7</th>
   </tr>
   <tr>
     <th scope="row">v6.x</th>
@@ -265,6 +266,7 @@ listed as supporting a later version.
     <td></td>
     <td></td>
     <td></td>
+    <td></td>
   </tr>
   <tr>
     <th scope="row">v8.x</th>
@@ -274,6 +276,7 @@ listed as supporting a later version.
     <td>v8.16.0</td>
     <td></td>
     <td></td>
+    <td></td>
   </tr>
   <tr>
     <th scope="row">v9.x</th>
@@ -283,6 +286,7 @@ listed as supporting a later version.
     <td></td>
     <td></td>
     <td></td>
+    <td></td>
   </tr>
   <tr>
     <th scope="row">v10.x</th>
@@ -292,6 +296,7 @@ listed as supporting a later version.
     <td>v10.16.0</td>
     <td>v10.17.0</td>
     <td>v10.20.0</td>
+    <td></td>
   </tr>
   <tr>
     <th scope="row">v11.x</th>
@@ -301,6 +306,7 @@ listed as supporting a later version.
     <td>v11.8.0</td>
     <td></td>
     <td></td>
+    <td></td>
   </tr>
   <tr>
     <th scope="row">v12.x</th>
@@ -310,6 +316,7 @@ listed as supporting a later version.
     <td>v12.0.0</td>
     <td>v12.11.0</td>
     <td>v12.17.0</td>
+    <td></td>
   </tr>
   <tr>
     <th scope="row">v13.x</th>
@@ -319,6 +326,7 @@ listed as supporting a later version.
     <td>v13.0.0</td>
     <td>v13.0.0</td>
     <td></td>
+    <td></td>
   </tr>
   <tr>
     <th scope="row">v14.x</th>
@@ -328,6 +336,7 @@ listed as supporting a later version.
     <td>v14.0.0</td>
     <td>v14.0.0</td>
     <td>v14.0.0</td>
+    <td>v14.12.0</td>
   </tr>
 </table>