Bump hystrix.version from 1.5.12 to 1.5.18

Bumps `hystrix.version` from 1.5.12 to 1.5.18.

Updates `hystrix-core` from 1.5.12 to 1.5.18
- [Release notes](https://github.com/Netflix/Hystrix/releases)
- [Changelog](https://github.com/Netflix/Hystrix/blob/master/CHANGELOG.md)
- [Commits](Netflix/Hystrix@v1.5.12...v1.5.18)

Updates `hystrix-metrics-event-stream` from 1.5.12 to 1.5.18
- [Release notes](https://github.com/Netflix/Hystrix/releases)
- [Changelog](https://github.com/Netflix/Hystrix/blob/master/CHANGELOG.md)
- [Commits](Netflix/Hystrix@v1.5.12...v1.5.18)

Updates `hystrix-codahale-metrics-publisher` from 1.5.12 to 1.5.18
- [Release notes](https://github.com/Netflix/Hystrix/releases)
- [Changelog](https://github.com/Netflix/Hystrix/blob/master/CHANGELOG.md)
- [Commits](Netflix/Hystrix@v1.5.12...v1.5.18)

pom.xml

@@ -52,7 +52,7 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <dropwizard.version>1.3.12</dropwizard.version>
-        <hystrix.version>1.5.12</hystrix.version>
+        <hystrix.version>1.5.18</hystrix.version>
         <slf4j.version>1.7.25</slf4j.version>
         <mockito.version>2.28.2</mockito.version>
         <junit.version>4.12</junit.version>