fix(docker): Force rebuild to get fixed ImageMagick packages

The build of ImageMagick that got built into the v0.10.8 Docker images
appears to be borked and is not handling PDF rasterization with embeded
fonts, it just throws garbage at the page.

Dockerfile

@@ -15,7 +15,7 @@ RUN pacman-key --recv-keys 63CC496475267693 && pacman-key --lsign-key 63CC496475
 # this as a separate layer because it saves time for local builds. Incrementing
 # this when pushing dependency updates to Caleb's Arch user repository or just
 # when the remote Docker Hub builds die should be enough.
-ARG DOCKER_HUB_CACHE=0
+ARG DOCKER_HUB_CACHE=1
 
 ARG RUNTIME_DEPS