gimp: Update version from 2.10.10 to 2.10.12

From the [announcement][1]:

> GIMP 2.10.12 is mostly a bug fix release as some annoying bugs were
> discovered, which is to be expected after a 2.10.10 with so many
> changes!
>
> Still, some very cool improvements are also available:
>
> *   Improved Curves tool
> *   Layers support for TIFF exporting
> *   Support for user-installed fonts on Windows
> *   Faster painting
> *   Improved symmetry painting support
> *   Incremental mode in the Dodge/Burn tool
> *   Free Select tool now creates a preliminary selection
> *   New Offset tool

[1]: https://www.gimp.org/news/2019/06/12/gimp-2-10-12-released/

gimp.be0

@@ -1,6 +1,6 @@
 #!/usr/bin/env beesh
 
-# BEE_VERSION gimp-2.10.10-0
+# BEE_VERSION gimp-2.10.12-0
 
 SRCURL[0]="https://download.gimp.org/mirror/pub/gimp/v${PKGVERSION[2]}/gimp-${PKGVERSION}.tar.bz2"