Use latest tag for devel image

[pallxk]

There're only latest and stable tags published to docker hub https://hub.docker.com/r/sivel/ansible-template-ui/tags.

And devel in UI corresponds to the latest tag.

ansible-template-ui/ansible_template_ui/client/index.html

Lines 72 to 75 in 043b560

	<ul class="dropdown-menu" uib-dropdown-menu role="menu" aria-labelledby="split-button">
	<li role="menuitem"><a href="#" ng-click="render()">Devel</a></li>
	<li role="menuitem"><a href="#" ng-click="render('stable')">Stable</a></li>
	</ul>

ansible-template-ui/ansible_template_ui/client/app.js

Line 26 in 043b560

var tag = tag || 'latest';

Hope this change makes it easier for newcomers to get started.