Gradle build fails

[sparkhead95]

openjdk version "1.8.0_191"
OpenJDK Runtime Environment (build 1.8.0_191-8u191-b12-2ubuntu0.18.04.1-b12)
OpenJDK 64-Bit Server VM (build 25.191-b12, mixed mode)

Grade build seems to be failing on Ubuntu 18.04:

FAILURE: Build failed with an exception.

* Where:
Script '/home/user/Projects/swagger2markup-cli/gradle/publishing.gradle' line: 25

* What went wrong:
Could not resolve all files for configuration ':compile'.
> Could not download logback-core.jar (ch.qos.logback:logback-core:1.1.2)
   > Could not get resource 'https://jcenter.bintray.com/ch/qos/logback/logback-core/1.1.2/logback-core-1.1.2.jar'.
      > Could not GET 'https://jcenter.bintray.com/ch/qos/logback/logback-core/1.1.2/logback-core-1.1.2.jar'. Received status code 504 from server: Gateway Time-out

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 3 mins 14.96 secs