Bump HikariCP-java6 from 2.3.8 to 2.3.13 in /modules/postgresql (#1051)

Bumps [HikariCP-java6](https://github.com/brettwooldridge/HikariCP) from 2.3.8 to 2.3.13.
<details>
<summary>Changelog</summary>

*Sourced from [HikariCP-java6's changelog](https://github.com/brettwooldridge/HikariCP/blob/dev/CHANGES).*

> HikariCP Changes
> 
> Changes in 3.2.0
> 
>  * check connection closed condition before attempting to set network timeout to avoid spurios exceptions
>    in the log.
> 
>  * updated validation failure message to include recommendation to check maxLifetime value.
> 
>  * fixed 1141 do not throw SQLException when calling isClosed() or close() on a already closed unwrapped
>    Connection, as per JDBC specification.
> 
>  * fixed 1137 support changing user/password at runtime for DriverDataSource-wrapped driver connections.
> 
>  * fixed 1136 log loaded driver when using jdbcUrl.
> 
>  * pull 1135 extract sealed pool check into independent method.
> 
>  * fixed 1126 correct error in JavaDoc for HikariConfig.setInitializationFailTimeout().
> 
>  * fixed 1114 removed unreachable code.
> 
> Changes in 3.1.0
> 
>  * Add get/setCatalog() to HikariConfigMXBean, allowing the catalog to be changed at runtime.
>    The catalog should only be changed while the pool is suspended, and after evicting existing
>    connections via HikariPoolMXBean.softEvictConnections().
> 
> Changes in 3.0.0
> 
>  * Removed previously deprecated methods;
>      HikariConfig.copyState()
>      HikariConfig.getScheduledExecutorService()
>      HikariConfig.setScheduledExecutorService()
>      HikariConfig.isInitializationFailFast()
>      HikariConfig.setInitializationFailFast()
>      HikariConfig.isJdbc4ConnectionTest()
>      HikariConfig.setJdbc4ConnectionTest()
> 
>      HikariDataSource.copyState()
>      HikariDataSource.getScheduledExecutorService()
>      HikariDataSource.setScheduledExecutorService()
>      HikariDataSource.suspendPool()
>      HikariDataSource.resumePool()
>      HikariDataSource.shutdown()
>      HikariDataSource.isInitializationFailFast()
>      HikariDataSource.setInitializationFailFast()
>      HikariDataSource.isJdbc4ConnectionTest()
>      HikariDataSource.setJdbc4ConnectionTest()
> 
></table> ... (truncated)
</details>
<details>
<summary>Commits</summary>

- [`390c569`](brettwooldridge/HikariCP@390c569) [maven-release-plugin] prepare release HikariCP-2.3.13
- [`e94d920`](brettwooldridge/HikariCP@e94d920) Fixes [#512](https://github-redirect.dependabot.com/brettwooldridge/HikariCP/issues/512) back port to 2.3.x stream.
- [`d5e496c`](brettwooldridge/HikariCP@d5e496c) [maven-release-plugin] prepare for next development iteration
- [`260ac29`](brettwooldridge/HikariCP@260ac29) [maven-release-plugin] prepare release HikariCP-2.3.12
- [`a312c5a`](brettwooldridge/HikariCP@a312c5a) Skip proxy generation during test runs
- [`f0ba4b7`](brettwooldridge/HikariCP@f0ba4b7) Fixed issue with new proxy class generation whereby Java 6 classes were gener...
- [`fe6eb41`](brettwooldridge/HikariCP@fe6eb41) [maven-release-plugin] prepare for next development iteration
- [`af5ba3b`](brettwooldridge/HikariCP@af5ba3b) [maven-release-plugin] prepare release HikariCP-2.3.11
- [`2c632e7`](brettwooldridge/HikariCP@2c632e7) Fixes major class version number for generated proxy classes.
- [`e2f1915`](brettwooldridge/HikariCP@e2f1915) [maven-release-plugin] prepare for next development iteration
- Additional commits viewable in [compare view](brettwooldridge/HikariCP@HikariCP-2.3.8...HikariCP-2.3.13)
</details>
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modules/postgresql/build.gradle

@@ -4,6 +4,6 @@ dependencies {
     compile project(':jdbc')
 
     testCompile 'org.postgresql:postgresql:9.3-1101-jdbc41'
-    testCompile 'com.zaxxer:HikariCP-java6:2.3.8'
+    testCompile 'com.zaxxer:HikariCP-java6:2.3.13'
     testCompile 'commons-dbutils:commons-dbutils:1.6'
 }