Update dependency cross-env to v7

Author: renovate-bot

package.json

@@ -85,7 +85,7 @@
     "babel-register": "6.26.0",
     "browser-sync": "2.24.7",
     "coveralls": "3.0.2",
-    "cross-env": "5.2.0",
+    "cross-env": "7.0.3",
     "eslint": "5.6.0",
     "eslint-config-standard": "12.0.0",
     "eslint-plugin-import": "2.14.0",