Update blah2.cpp

Cosmetic (as there's no further code to execute.. But terminating the t2 thread correctly.

src/blah2.cpp

@@ -307,7 +307,7 @@ int main(int argc, char **argv)
         }
       }
     });
-
+  t2.join();
   t1.join();
 
   return 0;
@@ -418,4 +418,4 @@ void timing_helper(std::vector<std::string>& timing_name,
   double delta_ms = (double)(time_us.back()-time_us[time_us.size()-2]) / 1000;
   timing_name.push_back(name);
   timing_time.push_back(delta_ms);
-}
+}