Merge pull request linuxkit#56 from ijc/portable-hash-updates

Portable `sed` expression for `make update-hashes`

Author: ijc

Makefile

@@ -32,7 +32,7 @@ update-hashes:
 	           $$(linuxkit pkg show-tag pkg/kubernetes-docker-image-cache-common) \
 	           $$(linuxkit pkg show-tag pkg/kubernetes-docker-image-cache-control-plane) ; do \
 	    image=$${tag%:*} ; \
-	    sed -i.bak -e "s,$$image:[[:xdigit:]]\{40\}\(-dirty\)\?,$$tag,g" yml/*.yml ; \
+	    sed -E -i.bak -e "s,$$image:[[:xdigit:]]{40}(-dirty)?,$$tag,g" yml/*.yml ; \
 	done
 
 .PHONY: clean