Update Mockttp to fix portfinder random proxy port bug

Author: pimterry

package-lock.json

@@ -40,7 +40,7 @@
     "graphql": "^14.0.2",
     "graphql-yoga": "^1.18.1",
     "lodash": "^4.17.13",
-    "mockttp": "^0.17.0",
+    "mockttp": "^0.17.1",
     "node-gsettings-wrapper": "^0.5.0",
     "osx-find-executable": "^1.0.0",
     "rimraf": "^2.6.2",