Fixed test issue in Simple.Data performance test (#723)

* Added fix for Simple.Data tast

Due to the missing .FirstOrDefault() in Simple.Data test, performance
numbers for Simple.Data were too high (better than hand coded data
reader). Added FirstOrDefault() to actually fetch the data.

Dapper.Tests/PerformanceTests.cs

@@ -255,7 +255,7 @@ public void Run(int iterations)
                 Try(() =>
                 {
                     var sdb = Simple.Data.Database.OpenConnection(TestSuite.ConnectionString);
-                    tests.Add(id => sdb.Posts.FindById(id), "Simple.Data");
+                    tests.Add(id => sdb.Posts.FindById(id).FirstOrDefault(), "Simple.Data");
                 }, "Simple.Data");
 #endif