fix(package): update strip-ansi to version 6.0.0

Closes #290

Author: greenkeeper[bot]

package.json

@@ -110,7 +110,7 @@
     "normalize-path": "^2.0.1",
     "progress": "^2.0.0",
     "source-map-support": "^0.5.0",
-    "strip-ansi": "^4.0.0",
+    "strip-ansi": "^6.0.0",
     "toposort": "^1.0.0",
     "yargs": "^11.0.0"
   },