CLJS-2662: Add Externs for Nashorn

Author: swannodette

src/main/cljs/cljs/externs.js

@@ -19,3 +19,9 @@ Object.prototype.next = function() {};
  */
 function IEquiv() {};
 IEquiv.prototype.equiv = function() {};
+
+/**
+ * @constructor
+ */
+function Java() {};
+Java.prototype.type = function() {};