Update mariadb

Changes:

- https://github.com/docker-library/mariadb/commit/c898836: Update to 1:10.3.15+maria~bionic

library/mariadb

@@ -9,9 +9,9 @@ Architectures: amd64, arm64v8, ppc64le
 GitCommit: 23417d54f56958b193e65ab548c34b3b336a1758
 Directory: 10.4
 
-Tags: 10.3.14-bionic, 10.3-bionic, 10-bionic, bionic, 10.3.14, 10.3, 10, latest
+Tags: 10.3.15-bionic, 10.3-bionic, 10-bionic, bionic, 10.3.15, 10.3, 10, latest
 Architectures: amd64, arm64v8, ppc64le
-GitCommit: 32aca58b13ee20d6514587e1a57ec9a0632fbe1d
+GitCommit: c89883655154c9f44891e7bd092232db646214b3
 Directory: 10.3
 
 Tags: 10.2.24-bionic, 10.2-bionic, 10.2.24, 10.2