fix(AMD-module): updating to enforce the AMD standard

https://github.com/amdjs/amdjs-api/blob/master/AMD.md designates that the factory should be a function.

c3.js

@@ -7091,7 +7091,7 @@
     }
 
     if (typeof define === 'function' && define.amd) {
-        define("c3", ["d3"], c3);
+        define("c3", ["d3"], function () { return c3; });
     } else if ('undefined' !== typeof exports && 'undefined' !== typeof module) {
         module.exports = c3;
     } else {