Stryker4s v0.6.1

Bugfixes

• Fix possible conflict with generated code in user's variable names (#239)

Other changes

• Update scalafmt 2.0.0 (#236)
• Update mutation-testing-elements, ... to 1.1.1 (#241)
• Update log4j-api, log4j-core, ... to 2.12.0 (#237)
• Update scalameta to 4.2.0 (#235)
• Add Stryker4s logo to readme
• Update sbt-scoverage to 1.6.0 (#231)