fix(deps): node-chartist is now an optional dependency and can be handled if missing

package.json

@@ -50,7 +50,6 @@
     "marked": "^4.0.17",
     "memory-cache": "^0.2.0",
     "minimatch": "^5.1.0",
-    "node-chartist": "^1.0.5",
     "node-fetch": "^3.2.6",
     "open-graph-scraper": "^4.11.1",
     "png-js": "^1.0.0",
@@ -79,6 +78,7 @@
   },
   "optionalDependencies": {
     "gifencoder": "^2.0.1",
-    "libxmljs2": "^0.30.1"
+    "libxmljs2": "^0.30.1",
+    "node-chartist": "^1.0.5"
   }
 }