build(package): require minimum node version: 8

Requires Node 8 due to updated picomatch dependency

BREAKING CHANGE: Node 7 and lower are no longer supported, Node 8 is now the minimum version

package.json

@@ -47,7 +47,7 @@
     "semantic-release": "^15.13.3"
   },
   "engines": {
-    "node": ">= 6.0.0"
+    "node": ">= 8.0.0"
   },
   "repository": {
     "type": "git",