build(dgeni): capital letter for selector (#4690)

* The label for the `selectors` should start with a capital letter. Similar as for the `Export as` label.

Author: devversion

tools/dgeni/templates/class.template.html

@@ -5,9 +5,9 @@ <h4 class="docs-api-h4 docs-api-class-name">
 
 {%- if class.directiveSelectors -%}
 <div class="docs-api-directive-selectors">
-  <span class="docs-api-class-selector-label">selector:</span>
-  {% for s in class.directiveSelectors %}
-    <span class="docs-api-class-selector-name">{$ s $}</span>
+  <span class="docs-api-class-selector-label">Selector:</span>
+  {% for selector in class.directiveSelectors %}
+    <span class="docs-api-class-selector-name">{$ selector $}</span>
   {% endfor %}
 </div>
 {%- endif -%}