Bump gitlab from 4.5.0 to 4.6.0

Bumps gitlab from 4.5.0 to 4.6.0.

Release notes

Sourced from gitlab's releases.

v4.6.0

General improvements

• Dropped Ruby 2.2 support
• Updated code style to comply with a community-driven Ruby coding style guide

Bugfixes

• Fixed handling interrupt signal on CLI
• Fixed passing hex color via CLI #414
• Fixed project events path #418

New features

• Added support for Diff versions API #403
• Added support for Merge Base API #405
• Added support for file uploads #412
• Added support for SSH keys for different users #413
• Added support for Version API #415

Commits

• cbc1397 Release v4.6.0
• 2911138 Merge pull request #418 from tudorpavel/fix-project-events-path
• 04d74b1 Fix project events path
• 8e9e321 Update rubocop config
• 55be321 Minor refactoring
• 5b9b45c Fix rubocop offense
• 5ad5091 Minor refactoring of client modules
• 4f0e930 Merge pull request #414 from szemek/create-label-hex-color
• 7c7dd33 Merge pull request #415 from codeship/add-version
• a2cfb7f Add support for Version API
• Additional commits viewable in compare view