Merge pull request #13 from nteract/fix-mdx

fixing up mdx

Author: rgbkrk

src/template/next.config.js

@@ -1,8 +1,11 @@
-const withMDX = require("@zeit/next-mdx")();
+const withMDX = require("@zeit/next-mdx")({
+  extension: /\.mdx?$/
+});
 module.exports = withMDX({
   exportPathMap: function() {
     return {
       "/": { page: "/" }
     };
-  }
+  },
+  pageExtensions: ["md", "mdx"]
 });