Log Message:
Update ImageMagick to 7.0.8.16.

The old distfile is no longer available upstream, and no one uploaded one :(

2018-12-02  7.0.8-16 Cristy  <quetzlzacatenango@image...>
  * Add support for -clahe clip limit with percentages (e.g. -clahe 2x2+128+3%)
  * Check for modulo underflow.
  * Change SVG default DPI to 96 from 90 to meet recommendation of SVG2 & CSS.