Update url_for from main.join to cloud.join

This text should be moved to Blender Cloud.

src/templates/projects/view.jade

@@ -115,7 +115,7 @@ link(href="{{ url_for('static_pillar', filename='assets/css/project-main.css', v
 					title="Search (subscribers only)",
 					data-toggle="tooltip",
 					data-placement="right")
-					a(href="{{ url_for('main.join') }}")
+					a(href="{{ url_for('cloud.join') }}")
 						i.pi-search
 				| {% endif %}
 				| {% endif %}