Update bash

Changes:

- https://github.com/tianon/docker-bash/commit/f643887: Update devel to 20201218, commit 3c5683a47b8ad7abd8232dee8a47d7c821904802

library/bash

@@ -3,9 +3,9 @@
 Maintainers: Tianon Gravi <[email protected]> (@tianon)
 GitRepo: https://github.com/tianon/docker-bash.git
 
-Tags: devel-20201214, devel
+Tags: devel-20201218, devel
 Architectures: amd64, arm32v6, arm32v7, arm64v8, i386, ppc64le, s390x
-GitCommit: b589273a1d10b1a3f994843f3cd3943f8fdbba68
+GitCommit: f6438876646f8e98ccc01f5bdbf5310768b8bda6
 Directory: devel
 
 Tags: 5.1.4, 5.1, 5, latest