Fixes #510 missing keyservers

Dockerfile

@@ -80,6 +80,10 @@ RUN if [[ "${RANKMIRRORS}" ]]; then \
         && cat /etc/pacman.d/mirrorlist \
     ; fi
 
+RUN tee -a /etc/pacman.d/gnupg/gpg.conf <<< 'keyserver hkp://keyserver.ubuntu.com' \
+    && tee -a /etc/pacman.d/gnupg/gpg.conf <<< 'keyserver hkps://hkps.pool.sks-keyservers.net:443' \
+    && tee -a /etc/pacman.d/gnupg/gpg.conf <<< 'keyserver hkp://pgp.mit.edu:11371'
+
 # This fails on hub.docker.com, useful for debugging in cloud
 # RUN [[ $(egrep -c '(svm|vmx)' /proc/cpuinfo) -gt 0 ]] || { echo KVM not possible on this host && exit 1; }