fix(core): load main scripts using relative paths

Using absolute urls only worked whe node-red was in top level directory.

src/nodes/core/index.ejs

@@ -1,6 +1,6 @@
-<script src="/node-red-contrib-z2m/editor/vendor.js"></script>
-<script src="/node-red-contrib-z2m/editor/core.js"></script>
-<script src="/node-red-contrib-z2m/editor/nodes.js"></script>
+<script src="node-red-contrib-z2m/editor/vendor.js"></script>
+<script src="node-red-contrib-z2m/editor/core.js"></script>
+<script src="node-red-contrib-z2m/editor/nodes.js"></script>
 <% if (env.NODE_ENV === 'development') { %>
 <script>
   (function () {