Bump postgresql from 42.2.15 to 42.2.18 (#2215)

Bumps [postgresql](https://github.com/pgjdbc/pgjdbc) from 42.2.15 to 42.2.18.
- [Release notes](https://github.com/pgjdbc/pgjdbc/releases)
- [Changelog](https://github.com/pgjdbc/pgjdbc/blob/REL42.2.18/CHANGELOG.md)
- [Commits](pgjdbc/pgjdbc@REL42.2.15...REL42.2.18)

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Author: dependabot[bot]

pom.xml

@@ -868,7 +868,7 @@
         <dependency>
             <groupId>org.postgresql</groupId>
             <artifactId>postgresql</artifactId>
-            <version>42.2.15</version>
+            <version>42.2.18</version>
         </dependency>
 
         <!-- Unit Testing Libraries -->