Fix bug horizontal scrollbar being pushed off page

We weren’t calculating the height quite right; we were trying to
compensate for something that should have been compensated for in the
`stick-at-top-when-scrolling` code.

Add the 5px to the shim there is required because we’re adding it to the
element that the shim in replacing.

app/assets/javascripts/fullscreenTable.js

@@ -62,7 +62,7 @@
     this.maintainHeight = () => {
 
       let height = Math.min(
-        $(window).height() - this.topOffset + $('html, body').scrollTop() + 5,
+        $(window).height() - this.topOffset + $('html, body').scrollTop(),
         this.nativeHeight
       );
 

app/assets/stylesheets/components/stick-at-top-when-scrolling.scss

@@ -53,4 +53,5 @@
 
 .shim {
   display: block;
+  margin-bottom: 5px;
 }