update ruby compatibility version

Author: jjb

index.html

@@ -19,7 +19,7 @@ <h3>The Best of the JVM</h3>
           <div class="feature ruby" id="feature_2">
             <h3>It's Just Ruby</h3>
 
-              Ruby 2.5 compatible
+              Ruby 2.6 compatible
 
           </div>
           <div class="feature platform" id="feature_3">