gthumb: Update version from 2.13.3 to 3.10.0

Update the almost nine year old version.

    $ ls -l /usr/bin/gthumb
    -rwxr-xr-x 1 root root 4419111 Oct 17  2011 /usr/bin/gthumb

Update the suffix for the LZMA compressed archive.

Maybe even the error below is fixed.

    /var/log/messages.2020-06:2020-05-05T08:38:30.842395+02:00 rocketraccoon kernel: [2403097.203273] pool-gthumb[25477]: segfault at 7fcdcd837c32 ip 00007fcdcd837c32 sp 00007fcdb7ffe730 error 14 in libfile_viewer.so[7fcdcda39000+3000]

gthumb.be0

@@ -1,8 +1,8 @@
 #!/usr/bin/env beesh
 
-# BEE_VERSION gthumb-2.13.3-0
+# BEE_VERSION gthumb-3.10.0-0
 
-SRCURL[0]="https://download.gnome.org/sources/gthumb/${PKGVERSION[2]}/gthumb-${PKGVERSION}.tar.bz2"
+SRCURL[0]="https://download.gnome.org/sources/gthumb/${PKGVERSION[2]}/gthumb-${PKGVERSION}.tar.xz"
 
 # PATCHURL+=()