Update Mockttp for lots of low-level bug fixes & perf tweaks

Author: pimterry

package-lock.json

@@ -84,7 +84,7 @@
     "mime-types": "^2.1.27",
     "mobx": "^6.3.5",
     "mockrtc": "^0.5.0",
-    "mockttp": "^4.2.1",
+    "mockttp": "^4.2.2",
     "node-fetch": "^2.6.1",
     "node-forge": "^1.3.2",
     "node-gsettings-wrapper": "^0.5.0",