Bump CentOS to 7.6.1810

Change-Id: If62c2faae4aa22e5b901352a323ee0f06e898f7d
diff --git a/centos/7/Dockerfile b/centos/7/Dockerfile
index 504de4a..40b8f1e 100644
--- a/centos/7/Dockerfile
+++ b/centos/7/Dockerfile
@@ -1,4 +1,4 @@
-FROM centos:7.5.1804
+FROM centos:7.6.1810
 MAINTAINER Gerrit Code Review Community
 
 # Add Gerrit packages repository
diff --git a/centos/7/Dockerfile-dev b/centos/7/Dockerfile-dev
index 0f19627..e34d8e2 100644
--- a/centos/7/Dockerfile-dev
+++ b/centos/7/Dockerfile-dev
@@ -1,4 +1,4 @@
-FROM centos:7.5.1804
+FROM centos:7.6.1810
 MAINTAINER Gerrit Code Review Community
 
 ARG GERRIT_WAR_URL="https://gerrit-ci.gerritforge.com/view/Gerrit/job/Gerrit-bazel-master/lastSuccessfulBuild/artifact/gerrit/bazel-bin/release.war"