Update Prometheus components

Update various Prometheus components to their upstream releases

• prometheus = 1.5.2
  • New minor upstream release, better memory use.
• gitlab-monitor = 1.2.0
  • New minor upstream release, improved CI metrics.
• postgres-exporter = 0.1.2
  • Bugfixes.
• redis-exporter = 0.10.7
  • Bugfixes.