ST7789: Replace gamma for 320x240 (PD2.0).

drivers/st7789/st7789.cpp

@@ -93,6 +93,8 @@ namespace pimoroni {
       command(reg::VCOMS, 1, "\x1f");
       //command(reg::GMCTRP1, 14, "\xD0\x08\x11\x08\x0C\x15\x39\x33\x50\x36\x13\x14\x29\x2D");
       //command(reg::GMCTRN1, 14, "\xD0\x08\x10\x08\x06\x06\x39\x44\x51\x0B\x16\x14\x2F\x31");
+      command(reg::GMCTRP1, 14, "\xd0\x00\x05\x0e\x15\x0d\x37\x43\x47\x09\x15\x12\x16\x19");
+      command(reg::GMCTRN1, 14, "\xd0\x00\x05\x0d\x0c\x06\x2d\x44\x40\x0e\x1c\x18\x16\x19");
     }
 
     if(width == 240 && height == 135) { // Pico Display Pack (1.14" 240x135)