Detect Gradle projects

What does this MR do?

This MR adds support for scanning gradle projects by bumping gemnasium-maven to v2.5.0 (updates project detection to scan build.gradle).

What are the relevant issue numbers?

gitlab-org/gitlab#13075 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• [-] Documentation created/updated for GitLab EE, if necessary
• [-] Documentation created/updated for this project, if necessary
• [-] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
• [-] Job definition updated, if necessary
  • [-] Job definition example
  • [-] CI Templates (to be removed)
  • [-] Vendored CI Templates (also in CE)
  • Ensure that all of the ENV vars supported are propagated to Docker containers upon docker run in job definitions
• [-] Conforms to the code review guidelines
• [-] Conforms to the Go guidelines
• [-] Security reports checked/validated by reviewer