configure jshint to allow ES6 Map constructor

.jshintrc

@@ -1,7 +1,7 @@
 {
 	"node": true, // Enable globals available when code is running inside of the NodeJS runtime environment.
 	"browser": true, // Standard browser globals e.g. `window`, `document`.
-	"esnext": false, // Allow ES.next specific features such as `const` and `let`.
+	"esversion": 6, // Allow ES.next specific features such as `const` and `let`.
 	"bitwise": false, // Prohibit bitwise operators (&, |, ^, etc.).
 	"camelcase": false, // Permit only camelcase for `var` and `object indexes`.
 	"curly": false, // Require {} for every new block or scope.