Add support for 1.12.2 compiled with ForgeGradle 3. (#73)

The latest 1.12.2 builds have been upgraded to ForgeGradle 3. Handling is slighly different, as the version.json
format is different and no longer stored in the universal jar. You have to provide the version.json as a VersionManifest
module, the same as 1.13+. The rest of the launch handling hasn't changed.

Nebula supports the new 1.12.2 format.

package.json

@@ -41,8 +41,8 @@
   },
   "devDependencies": {
     "cross-env": "^7.0.2",
-    "electron": "^9.0.0",
-    "electron-builder": "^22.6.1",
+    "electron": "^9.0.2",
+    "electron-builder": "^22.7.0",
     "eslint": "^7.1.0"
   },
   "repository": {