Fix mouse button processing in plotter

Turns out that I'd reversed the logic for a couple of the fields. The
current plotter also doesn't actually use either the middle click or
right click buttons, so this didn't actually matter.

Change-Id: I51d552b332318f4b4069784cf77458a34b79842d
diff --git a/aos/network/www/plotter.ts b/aos/network/www/plotter.ts
index 4a51c34..c10ff80 100644
--- a/aos/network/www/plotter.ts
+++ b/aos/network/www/plotter.ts
@@ -199,9 +199,9 @@
     case 0:
       return MouseButton.Left;
     case 1:
-      return MouseButton.Right;
-    case 2:
       return MouseButton.Middle;
+    case 2:
+      return MouseButton.Right;
   }
 }
 
@@ -212,9 +212,9 @@
     // we would expect them to be given the .button field.
     case MouseButton.Left:
       return 0 !== (event.buttons & 0x1);
-    case MouseButton.Middle:
-      return 0 !== (event.buttons & 0x2);
     case MouseButton.Right:
+      return 0 !== (event.buttons & 0x2);
+    case MouseButton.Middle:
       return 0 !== (event.buttons & 0x4);
   }
 }