adds modal heading modifier that removes margin

opentech/apply/funds/templates/funds/includes/batch_update_reviewer_form.html

 <div class="modal" id="batch-update-reviewers">
-    <h4 class="modal__header-bar">Add Reviewers</h4>
+    <h4 class="modal__header-bar modal__header-bar--no-bottom-space">Add Reviewers</h4>
     <div class="modal__list-item modal__list-item--meta" aria-live="polite">
         <span class="js-batch-title-count"></span>
         <a href="#" class="modal__hide-link js-toggle-batch-list">Show</a>

opentech/static_src/src/sass/apply/components/_modal.scss

@@ -12,9 +12,13 @@
     &__header-bar {
         color: $color--white;
         background-color: $color--dark-blue;
-        margin: -24px -24px 0;
+        margin: -24px -24px 20px;
         padding: 15px;
         text-align: center;
+
+        &--no-bottom-space {
+            margin-bottom: 0;
+        }
     }
 
     &__list {