package/imagemagick: change download url to github

Upstream quickly removes old versions from
http://www.imagemagick.org/download/releases

For our LTS versions we should switch to a stable upstream repo which
provides all released versions.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/imagemagick/imagemagick.hash

@@ -1,2 +1,2 @@
-# From http://www.imagemagick.org/download/releases/digest.rdf
-sha256 0058fcde533986334458a5c99600b1b9633182dd9562cbad4ba618c5ccf2a28f  ImageMagick-7.0.5-10.tar.xz
+# Locally computed
+sha256 bd965d36a65cbcd420ec79a509a5ce0ecdfef036770cdc87fcd5374b9ed15ea7  7.0.5-10.tar.gz

package/imagemagick/imagemagick.mk

@@ -5,8 +5,8 @@
 ################################################################################
 
 IMAGEMAGICK_VERSION = 7.0.5-10
-IMAGEMAGICK_SOURCE = ImageMagick-$(IMAGEMAGICK_VERSION).tar.xz
-IMAGEMAGICK_SITE = http://www.imagemagick.org/download/releases
+IMAGEMAGICK_SOURCE = $(IMAGEMAGICK_VERSION).tar.gz
+IMAGEMAGICK_SITE = https://github.com/ImageMagick/ImageMagick/archive
 IMAGEMAGICK_LICENSE = Apache-2.0
 IMAGEMAGICK_LICENSE_FILES = LICENSE