Remove treshold from IntersectionObserver

As content inserted to Common Page may be longer, it can be possible
that 70% of content will never be visible at once, and thus content
will never be visible. Remove threshold to mitigate this issue.

Author: PeeterPaal

javascripts/application.js

@@ -855,9 +855,6 @@
                 entry.target.classList.add('visible');
               }
             });
-          },
-          {
-            threshold: 0.7,
           }
         );