Update to latest electron builder

Tested auto update on both windows (ia32) and mac, seems to work!

package.json

@@ -100,8 +100,8 @@
     "concurrently": "^4.0.1",
     "cpx": "^1.3.2",
     "cross-env": "^4.0.0",
-    "electron-builder": "^11.2.4",
-    "electron-builder-squirrel-windows": "^11.2.1",
+    "electron-builder": "^20.28.4",
+    "electron-builder-squirrel-windows": "^11.6.1",
     "electron-devtools-installer": "^2.2.4",
     "emojione": "^2.2.7",
     "eslint": "^5.6.0",
@@ -150,12 +150,7 @@
   },
   "build": {
     "appId": "im.riot.app",
-    "category": "Network",
     "electronVersion": "3.0.3",
-    "//asar=false": "https://github.com/electron-userland/electron-builder/issues/675",
-    "asar": false,
-    "dereference": true,
-    "//files": "We bundle everything, so we only need to include webapp/",
     "files": [
       "node_modules/**",
       "src/**",
@@ -172,8 +167,13 @@
         "StartupWMClass": "riot"
       }
     },
+    "mac": {
+      "category": "public.app-category.social-networking"
+    },
     "win": {
-      "target": "squirrel"
+      "target": {
+        "target": "squirrel"
+      }
     },
     "directories": {
       "buildResources": "electron_app/build",