Update to electron-builder 21.0.15

package.json

@@ -29,7 +29,7 @@
     },
     "devDependencies": {
         "electron": "5.0.5",
-        "electron-builder": "20.44.4",
+        "electron-builder": "21.0.15",
         "eslint": "6.0.1",
         "xmldom": "0.1.27"
     }