doc: set module version 72 to node 12

Clearly state the modules version 72 is official node 12, similar as it
is done for other major node versions.

PR-URL: #29877
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

doc/abi_version_registry.json

@@ -4,7 +4,7 @@
     { "modules": 75, "runtime": "electron", "variant": "electron",             "versions": "7" },
     { "modules": 74, "runtime": "node",     "variant": "v8_7.5",               "versions": "13.0.0-pre" },
     { "modules": 73, "runtime": "electron", "variant": "electron",             "versions": "6" },
-    { "modules": 72, "runtime": "node",     "variant": "v8_7.4",               "versions": "12.0.0-pre" },
+    { "modules": 72, "runtime": "node",     "variant": "node",                 "versions": "12" },
     { "modules": 71, "runtime": "node",     "variant": "v8_7.3",               "versions": "12.0.0-pre" },
     { "modules": 70, "runtime": "electron", "variant": "electron",             "versions": "5" },
     { "modules": 69, "runtime": "electron", "variant": "electron",             "versions": "^4.0.4" },