Replace karma with jsdom + mocha + chai

* Also a bit refactoring for better testability

src/js/utils/renderer.js

@@ -0,0 +1,20 @@
+
+export function render(repository, commits) {
+  const $commits = commits.map(commit => {
+    return `
+      <li>
+        <span>${commit.message.replace(/\n/g, '<br />')}<span>
+        <br /><br />
+        <small>${commit.committer.name}</small>
+      </li>`;
+  });
+
+  return `
+    <h1>${repository.description}</h1>
+    <h2>
+      <a href="${repository.html_url}">${repository.full_name}</a>
+    </h2>
+    <ul>${$commits.join('')}</ul>
+  `;
+}
+