php-imagick: bump version to 3.4.3RC1
This version is marked as "stable" on php-imagick's website, plus is
necessary for the upcoming php-7.1 version bump.
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>