add missing Oxford comma

Author: michaelficarra

index.html

@@ -76,7 +76,7 @@ <h2>Stages</h2>
       <ul>
         <li>Identified a champion or champion group who will advance the addition
         <li>Prose outlining the problem or need and the general shape of a solution
-        <li>Discussion of key algorithms, abstractions and semantics
+        <li>Discussion of key algorithms, abstractions, and semantics
         <li>Identification of potential cross-cutting concerns and implementation challenges/complexity
         <li>A publicly available repository for the proposal that captures the above requirements
       </ul>