Include Observable.count test;

tests/observable.lua

@@ -186,6 +186,7 @@ describe('Observable', function()
   dofile('tests/compact.lua')
   dofile('tests/concat.lua')
   dofile('tests/contains.lua')
+  dofile('tests/count.lua')
   dofile('tests/distinct.lua')
   dofile('tests/distinctUntilChanged.lua')
   dofile('tests/filter.lua')