Ensure to pass Map.prototype as map

Author: medikoo

is-map.js

@@ -7,6 +7,6 @@ var toStringTagSymbol = require('es6-symbol').toStringTag
   , Global = (typeof Map === 'undefined') ? null : Map;
 
 module.exports = function (x) {
-	return (x && ((Global && (x instanceof Global)) ||
+	return (x && ((Global && ((x instanceof Global) || (x === Global.prototype))) ||
 			(toString.call(x) === id) || (x[toStringTagSymbol] === 'Map'))) || false;
 };