Fixing deep dependency problem with node 6.x

this commit has been blatantly stolen from @samselikoff in ember-cli-addon-docs. It prevents an issue introduced via a deep dependency that no longer supports node 6 (which we still would like to support).
see: ember-learn/ember-cli-addon-docs@231275b
see: salesforce/tough-cookie#141

Signed-off-by: Claudius Coenen <opensource@amenthes.de>

Author: ccoenen

package.json

@@ -132,6 +132,9 @@
     "ws": "^6.0.0",
     "xss": "^1.0.3"
   },
+  "resolutions": {
+    "**/tough-cookie": "~2.4.0"
+  },
   "engines": {
     "node": ">=6.x"
   },