Add snap support to packages.json. (#1503)

package.json

@@ -74,7 +74,8 @@
       "target": [
         "deb",
         "AppImage",
-        "rpm"
+        "rpm",
+        "snap"
       ]
     },
     "win": {
@@ -84,6 +85,10 @@
     },
     "mac": {
       "category": "public.app-category.developer-tools"
+    },
+    "snap": {
+      "confinement": "classic",
+      "grade": "stable"
     }
   },
   "license": "MIT",
@@ -126,7 +131,7 @@
     "copy-webpack-plugin": "^4.0.0",
     "cross-env": "3.1.3",
     "electron": "1.4.7",
-    "electron-builder": "8.6.0",
+    "electron-builder": "13.6.0",
     "electron-devtools-installer": "^2.0.0",
     "electron-rebuild": "1.5.6",
     "eslint-config-xo-react": "^0.10.0",