Fix outdated GraphicsGale URL (#137) (#138)

Author: djedditt

content/objbg.md

@@ -164,7 +164,7 @@ Sprites and backgrounds have separate palettes. The background palette goes firs
 
 In 8-bit color mode, the pixel value in the tiles is palette-index for that pixel. In 4-bit color mode, the pixel value contains the lower nybble of the palette index; the high nybble is the <dfn>palbank</dfn> index, which can be found in either the sprite's attributes, or the upper nybble of the tiles. If the pixel-value is 0, then that pixel won't be rendered (i.e., will be transparent).
 
-Because of 16-color mode and the transparency issue, it is *essential* that your bitmap editor leaves the palette intact. I know from personal experience that MS-Paint and the Visual C bitmap editor don't, so you might want to use something else. Favorites among other GBA developers are [Graphics Gale](http://www.tempest-j.com/gale/e/) and [GIMP](http://www.gimp.org). Of course, since I have my [my own bitmap editor](http://www.coranac.com/projects/#usenti), I prefer to use that.
+Because of 16-color mode and the transparency issue, it is *essential* that your bitmap editor leaves the palette intact. I know from personal experience that MS-Paint and the Visual C bitmap editor don't, so you might want to use something else. Favorites among other GBA developers are [Graphics Gale](https://graphicsgale.com/us/) and [GIMP](http://www.gimp.org). Of course, since I have my [my own bitmap editor](http://www.coranac.com/projects/#usenti), I prefer to use that.
 
 ## Summary {#sec-summary}