Update render-svg.sh to ImageMagick 7

MxCravenrequested to merge
MxCraven/mediasource:render-svg into master

The convert command was depricated in ImageMagick 7 (released in at least 2016) and replaced with magick. This script gives WARNING: The convert command is deprecated in IMv7, use "magick" instead of "convert" or "magick convert" and will fail if convert isn't aliased.

Updated the convert line, and changed the dependency versions to the ones tested with (though this should work on any IMv7)

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