Fixed lowercase change missing on commit a22a228b.

Servo.cpp and Servo.h were changed to lowercase in Makefile but not their actual filenames.

Marlin/Marlin_main.cpp

 #endif
 
 #if NUM_SERVOS > 0
-  #include "Servo.h"
+  #include "servo.h"
 #endif
 
 #if HAS_DIGIPOTSS

Marlin/Servo.cpp → Marlin/servo.cpp

 #include <avr/interrupt.h>
 #include <Arduino.h>
 
-#include "Servo.h"
+#include "servo.h"
 
 #define usToTicks(_us)    (( clockCyclesPerMicrosecond()* _us) / 8)     // converts microseconds to tick (assumes prescale of 8)  // 12 Aug 2009
 #define ticksToUs(_ticks) (( (unsigned)_ticks * 8)/ clockCyclesPerMicrosecond() ) // converts from ticks back to microseconds