feat: require node >= 8.10

BREAKING CHANGE: support for node 4, 6, and < 8.10 has been dropped.

Author: haltcase

package.json

@@ -8,7 +8,7 @@
   "homepage": "https://github.com/citycide/tablemark",
   "bugs": "https://github.com/citycide/tablemark/issues",
   "engines": {
-    "node": ">=4"
+    "node": ">=8.10"
   },
   "keywords": [
     "markdown",