Update alpine Docker tag to v3.13.4 (#506)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

docker/batch-change-volume-workspace/Dockerfile

@@ -2,6 +2,6 @@
 # image that we use to run curl, git, and unzip against a Docker volume when
 # using the volume workspace.
 
-FROM alpine:3.13.2@sha256:a75afd8b57e7f34e4dad8d65e2c7ba2e1975c795ce1ee22fa34f8cf46f96a3be
+FROM alpine:3.13.4@sha256:ec14c7992a97fc11425907e908340c6c3d6ff602f5f13d899e6b7027c9b4133a
 
 RUN apk add --update git unzip