Update update.cpp

fixed issue #206

src/update.cpp

@@ -3,7 +3,7 @@ this file copied from esp32-arduino library and patched, see PR
 https://github.com/espressif/arduino-esp32/pull/1979
 */
 
-#include "Update.h"
+#include "update.h"
 #include "Arduino.h"
 #include "esp_spi_flash.h"
 #include "esp_ota_ops.h"
@@ -372,4 +372,4 @@ void UpdateClass::printError(Stream &out){
     out.println(_err2str(_error));
 }
 
-UpdateClass Update;
+UpdateClass Update;