fix(coverage): always send a result object

This is just a fix for stable, in the master I will change the implementation,
so that the "testacular" is responsible for sending the coverage results, 
rather than individual adapters.

Closes #365

static/testacular.src.js

@@ -89,7 +89,7 @@ var Testacular = function(socket, context, navigator, location) {
   };
 
   this.complete = function(result) {
-    socket.emit('complete', result);
+    socket.emit('complete', result || {});
     clearContext();
   };