package/imagemagick: security bump to version 7.0.8-42

package/imagemagick: security bump to version 7.0.8-42

Fixes the following security issues:

- CVE-2019-9956: In ImageMagick 7.0.8-35 Q16, there is a stack-based buffer
  overflow in the function PopHexPixel of coders/ps.c, which allows an
  attacker to cause a denial of service or code execution via a crafted
  image file.

- CVE-2019-10650: In ImageMagick 7.0.8-36 Q16, there is a heap-based buffer
  over-read in the function WriteTIFFImage of coders/tiff.c, which allows an
  attacker to cause a denial of service or information disclosure via a
  crafted image file.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>