fix(package.json): add "resolutions" field to prevent two Cypress vers

@testing-library/cypress was downloading another version of Cypress;
This would conflict with our installed version and crash on Travis CI;

References:
github.com/cypress-io/cypress/issues/4595

package.json

@@ -20,6 +20,9 @@
     "test": "cypress run",
     "test:cypress": "cypress open"
   },
+  "resolutions": {
+    "cypress": "4.9.0"
+  },
   "dependencies": {
     "@material-ui/core": "^4.9.10",
     "@material-ui/icons": "^4.9.1",