PID: fix example using wrong type

pid.imax() has type int16_t

../../libraries/PID/examples/pid/pid.cpp:36:53: warning: format ‘%f’ expects argument of type ‘double’, but argument 6 has type ‘int’ [-Wformat=]
             pid.kP(), pid.kI(), pid.kD(), pid.imax());
                                                     ^

libraries/PID/examples/pid/pid.cpp

@@ -32,7 +32,7 @@ void setup()
     pid.imax(0);
     pid.load_gains();
     hal.console->printf(
-            "P %f  I %f  D %f  imax %f\n",
+            "P %f  I %f  D %f  imax %d\n",
             pid.kP(), pid.kI(), pid.kD(), pid.imax());
 }