Fix compile error in sample code: PinHistory does not understand size(), but does understand queueSize().

Author: James Foster

REFERENCE.md

@@ -311,7 +311,7 @@ unittest(pin_history)
   // we expect 6 values in that queue (5 that we set plus one
   // initial value), which we'll hard-code here for convenience.
   // (we'll actually assert those 6 values in the next block)
-  assertEqual(6, state->digitalPin[1].size());
+  assertEqual(6, state->digitalPin[1].queueSize));
   bool expected[6] = {LOW, HIGH, LOW, LOW, HIGH, HIGH};
   bool actual[6];