Switch to forked frisby.js where keep-alive connections are turned off

(fixes #2068)

package.json

@@ -242,7 +242,7 @@
     "eslint-plugin-import": "^2.28.1",
     "eslint-plugin-node": "^11.1.0",
     "eslint-plugin-promise": "^6.1.1",
-    "frisby": "^2.1.3",
+    "frisby": "https://github.com/bkimminich/frisby.git",
     "grunt-cli": "^1.3.2",
     "http-server": "^0.12.3",
     "jasmine": "^3.9.0",