add enter key listener to robot ID input

sumorobot.js

@@ -511,6 +511,14 @@ window.onload = function() {
         workspace.highlightBlock(lastHighlighted, false);
     });
 
+    /* enter listener on robot ID field */
+    $("#robot-id").keypress(function(e) {
+        if (e.which == 13) {
+            /* simulate robot GO button click */
+            $(".btn-robot-go").click();
+        }
+    });
+
     /* robot number button listener */
     $(".btn-robot-go").click(function() {
         /* extract and validate the selected robot ID */