Update memcached

Changes:

- https://github.com/docker-library/memcached/commit/7b4e8f0: Update to 1.5.19
- https://github.com/docker-library/memcached/commit/c796c3f: Update generated README

library/memcached

@@ -4,12 +4,12 @@ Maintainers: Tianon Gravi <[email protected]> (@tianon),
              Joseph Ferguson <[email protected]> (@yosifkit)
 GitRepo: https://github.com/docker-library/memcached.git
 
-Tags: 1.5.17, 1.5, 1, latest
+Tags: 1.5.19, 1.5, 1, latest
 Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, ppc64le, s390x
-GitCommit: 3b01d6e4e0ccc504e0db13ccf3c574481fe6f801
+GitCommit: 7b4e8f0188c2f4565f8077c584680df6a93bc263
 Directory: debian
 
-Tags: 1.5.17-alpine, 1.5-alpine, 1-alpine, alpine
+Tags: 1.5.19-alpine, 1.5-alpine, 1-alpine, alpine
 Architectures: amd64, arm32v6, arm32v7, arm64v8, i386, ppc64le, s390x
-GitCommit: 3b01d6e4e0ccc504e0db13ccf3c574481fe6f801
+GitCommit: 7b4e8f0188c2f4565f8077c584680df6a93bc263
 Directory: alpine