Polish contribution

Closes gh-6534

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/JdbcSessionDatabaseInitializer.java

@@ -45,6 +45,7 @@ public class JdbcSessionDatabaseInitializer {
 		aliases.put("apache derby", "derby");
 		aliases.put("hsql database engine", "hsqldb");
 		aliases.put("microsoft sql server", "sqlserver");
+		aliases.put("postgres", "postgresql");
 		ALIASES = Collections.unmodifiableMap(aliases);
 	}