Update mockttp and fix package.json importing

Author: pimterry

custom-typings/package.json.d.ts

@@ -27,7 +27,7 @@
     "env-paths": "^1.0.0",
     "graphql-yoga": "^1.16.7",
     "lodash": "^4.17.11",
-    "mockttp": "^0.11.0",
+    "mockttp": "^0.12.2",
     "rimraf": "^2.6.2",
     "tslib": "^1.9.3"
   },

package-lock.json

@@ -7,6 +7,7 @@
         "outDir": "lib",
         "strict": true,
         "target": "es2017",
+        "resolveJsonModule": true,
         "composite": true,
         "typeRoots" : [
             "./node_modules/@types",