Make the devserver serve from the proper location.

tests/index.html

@@ -11,7 +11,7 @@
         <script src="https://unpkg.com/mocha@4.0.1/mocha.js"></script>
 
         <script>mocha.setup('bdd')</script>
-        <script type="module" src="../tests.bundle.js"></script>
+        <script type="module" src="../dist/tests.bundle.js"></script>
         <script type="module">
             mocha.checkLeaks();
             mocha.run();