Work around installation of dependencies of mock-server in non-local environments (#398)

Author: LexLuengas

package.json

@@ -41,7 +41,7 @@
     "package": "npx yarn pack --filename openapi-cop.tgz",
     "preinstall": "npx per-env",
     "preinstall:production": "",
-    "preinstall:development": "cd mock-server && npm install"
+    "preinstall:development": "(test -d mock-server && cd mock-server && npm install) || true"
   },
   "dependencies": {
     "@types/express": "4.17.13",