update actions and dependencies

What’s Changed

🕸Dependencies:

• Updates #22 (@mimmi20)
• github-actions(deps): bump actions/cache from v2.1.1 to v2.1.2 #20 (@dependabot[bot])
• Build(deps): Update slevomat/coding-standard requirement from ~6.4.0 to ~6.4.1 #19 (@dependabot[bot])

🧹Maintenance:

• Update dependabot.yml #21 (@mimmi20)