Update dependency cross-env to v6

Author: renovate-bot

package-lock.json

@@ -58,7 +58,7 @@
     "chai-fs": "^2.0.0",
     "chai-string": "^1.5.0",
     "cpr": "^3.0.1",
-    "cross-env": "^5.0.1",
+    "cross-env": "^6.0.0",
     "ember-cli": "3.13.0",
     "ember-cli-addon-tests": "0.11.1",
     "eslint": "^6.1.0",