Remove non-POSIX loop construct

ci/run-docker.sh

@@ -9,11 +9,10 @@ run() {
     echo "Building docker container for target ${1}"
 
     # FIXME: Hacky workaround. Docker build seems to work better if we pull the base images first
-    ubuntu_images=( 16.04 17.10 18.04 )
-    for i in "${ubuntu_images[@]}"
-    do
-      docker pull ubuntu:$i
-    done
+    # Not using arrays/loops because it's not POSIX sh compatible
+    docker pull ubuntu:16.04
+    docker pull ubuntu:17.10
+    docker pull ubuntu:18.04
 
     # use -f so we can use ci/ as build context
     docker build -t libc -f "ci/docker/${1}/Dockerfile" ci/