update instructions for stable branch

Author: akkartik

index.md

@@ -21,7 +21,7 @@ title: Arc Programming Language
 <span style='color:grey'>$</span> git clone <a href='http://github.com/arclanguage/anarki'>http://github.com/arclanguage/anarki</a>
 <span style='color:grey'>$</span> git checkout stable
 <span style='color:grey'>$</span> cd anarki
-<span style='color:grey'>$</span> ./arc.sh
+<span style='color:grey'>$</span> ./arc
 <span style='color:grey'>arc&gt;</span> (quit)
 <span style='color:grey'>$</span></pre>
     <div style='font-size:small'>(<a href='http://arclanguage.org/install'>Official and outdated instructions.</a>)</div>