Update Mockttp for request body race condition fix

Author: pimterry

package-lock.json

@@ -86,7 +86,7 @@
     "mime-types": "^2.1.27",
     "mobx": "^6.3.5",
     "mockrtc": "^0.5.1",
-    "mockttp": "^4.3.0",
+    "mockttp": "^4.3.1",
     "node-fetch": "^2.6.1",
     "node-forge": "^1.4.0",
     "node-gsettings-wrapper": "^0.5.0",