Update gfxfont.h (#286)

gfxfont.h

@@ -21,8 +21,8 @@ typedef struct {
 typedef struct {
   uint8_t *bitmap;  ///< Glyph bitmaps, concatenated
   GFXglyph *glyph;  ///< Glyph array
-  uint8_t first;    ///< ASCII extents (first char)
-  uint8_t last;     ///< ASCII extents (last char)
+  uint16_t first;   ///< ASCII extents (first char)
+  uint16_t last;    ///< ASCII extents (last char)
   uint8_t yAdvance; ///< Newline distance (y axis)
 } GFXfont;