Update memcached

Changes:

- https://github.com/docker-library/memcached/commit/42ae787: Merge pull request https://github.com/docker-library/memcached/pull/52 from blar/patch-1
- https://github.com/docker-library/memcached/commit/8b8b8af: Add "--no-network" to all "apk add" invocations that don't need network
- https://github.com/docker-library/memcached/commit/b590c55: Reduce image size

library/memcached

@@ -11,5 +11,5 @@ Directory: debian
 
 Tags: 1.5.16-alpine, 1.5-alpine, 1-alpine, alpine
 Architectures: amd64, arm32v6, arm32v7, arm64v8, i386, ppc64le, s390x
-GitCommit: 97c659e9dae9b5f907783d31afdc4e98076b37c5
+GitCommit: 8b8b8af37c2c6ee65e2c2b1a53c296114f0ae6ae
 Directory: alpine