doc: claim NODE_MODULE_VERSION=76 for Electron 8

PR-URL: nodejs#28809
Refs: https://github.com/electron/electron/projects/20#card-24099810
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

doc/abi_version_registry.json

@@ -1,5 +1,6 @@
 {
   "NODE_MODULE_VERSION": [
+    { "modules": 76, "runtime": "electron", "variant": "electron",             "versions": "8" },
     { "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" },