Support typescript files until netlify/pull/39 is merged

Author: stefan--

lib/build.js

@@ -74,8 +74,8 @@ function webpackConfig(dir, additionalConfig) {
     devtool: false
   };
   fs.readdirSync(dirPath).forEach(function(file) {
-    if (file.match(/\.js$/)) {
-      var name = file.replace(/\.js$/, "");
+    if (file.match(/\.(m?js|ts)$/)) {
+      var name = file.replace(/\.(m?js|ts)$/, "");
       webpackConfig.entry[name] = "./" + name;
     }
   });