Restore Wire pins

Restore Wire pins which got lost during bcmi-labs/ArduinoCore-avr-api@3a86847

Author: facchinm

variants/uno2018/pins_arduino.h

@@ -46,8 +46,8 @@ static const uint8_t MOSI = PIN_SPI_MOSI;
 static const uint8_t MISO = PIN_SPI_MISO;
 static const uint8_t SCK  = PIN_SPI_SCK;
 
-#define PIN_WIRE_SDA        (18)
-#define PIN_WIRE_SCL        (19)
+#define PIN_WIRE_SDA        (20)
+#define PIN_WIRE_SCL        (21)
 
 static const uint8_t SDA = PIN_WIRE_SDA;
 static const uint8_t SCL = PIN_WIRE_SCL;