chore(tests): Use yarn workspace for test:downstream.

Author: christopherthielen

package.json

@@ -11,7 +11,7 @@
     "build": "run-s compile bundle fixmaps:*",
     "release": "release --deps @uirouter/core",
     "test": "karma start",
-    "test:downstream": "npm run build && test_downstream_projects",
+    "test:downstream": "npm run build && test_downstream_projects --workspace",
     "debug": "karma start --singleRun=false --autoWatch=true --autoWatchInterval=1 --browsers=Chrome",
     "package": "npm run build",
     "docs": "generate_docs && publish_docs",