graphics/ImageMagick7: update to 7.1.0-18

graphics/ImageMagick7/Makefile

 PORTNAME=	ImageMagick
-DISTVERSION=	7.1.0-17
+DISTVERSION=	7.1.0-18
 CATEGORIES=	graphics perl5
 MASTER_SITES=	https://www.imagemagick.org/download/ \
 		https://www.imagemagick.org/download/releases/ \

graphics/ImageMagick7/distinfo

-TIMESTAMP = 1639247749
-SHA256 (ImageMagick-7.1.0-17.tar.xz) = af4c2992b2edd7f2979a4bb26e4d47baf7ac0cce190ca1d4678fb4bd318d9589
-SIZE (ImageMagick-7.1.0-17.tar.xz) = 10323340
+TIMESTAMP = 1640511740
+SHA256 (ImageMagick-7.1.0-18.tar.xz) = befd78492ebcf31202c214b05494f37f561738ed4d26d7f197ee2f2142b2bf7d
+SIZE (ImageMagick-7.1.0-18.tar.xz) = 10313792