Bump postgresql from 42.2.6 to 42.2.8

Bumps [postgresql](https://github.com/pgjdbc/pgjdbc) from 42.2.6 to 42.2.8.
- [Release notes](https://github.com/pgjdbc/pgjdbc/releases)
- [Changelog](https://github.com/pgjdbc/pgjdbc/blob/master/CHANGELOG.md)
- [Commits](pgjdbc/pgjdbc@REL42.2.6...REL42.2.8)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

build.gradle

@@ -150,7 +150,7 @@ dependencies {
 
     compile group: 'org.mariadb.jdbc', name: 'mariadb-java-client', version: '2.4.3'
 
-    compile 'org.postgresql:postgresql:42.2.6'
+    compile 'org.postgresql:postgresql:42.2.8'
 
     compile ('com.google.guava:guava:28.1-jre') {
         // TODO: Remove this as soon as https://github.com/google/guava/issues/2960 is fixed