ImageMagick: update to 7.0.8.40.

2019-04-12  7.0.8-40 Cristy  <quetzlzacatenango@image...>
  * Release ImageMagick version 7.0.8-40, GIT revision 15513:1a235853a:20190412

2019-04-10  7.0.8-40 Cristy  <quetzlzacatenango@image...>
  * Fixed a number of issues (reference
    https://imagemagick.org/discourse-server/viewforum.php?f=3).
  * Fixed a number of issues (reference
    https://github.com/ImageMagick/ImageMagick/issues).

2019-04-07  7.0.8-39 Cristy  <quetzlzacatenango@image...>
  * Release ImageMagick version 7.0.8-39, GIT revision 15489:6120f8bc1:20190406

2019-04-06  7.0.8-39 Cristy  <quetzlzacatenango@image...>
  * The -layers option compared pixels inocorrectly as opacity rather than
    alpha.
  * The -preview raise option now returns expected results.
  * Initialise ghostscript instances with NULL (reference
    https://github.com/ImageMagick/ImageMagick/pull/1538).

(wiz)