Set VERSION to 1.6.1 (JuliaLang#40507)

release-1.6: set VERSION to 1.6.0 (JuliaLang#40162)

 release-1.6: set VERSION to 1.6-rc3 (JuliaLang#40060)

release-1.6: set VERSION to 1.6-rc2 (JuliaLang#39977)

Set VERSION to 1.5.4 (JuliaLang#39827)

release-1.6: set VERSION to 1.6-rc1 (JuliaLang#39487)

Set VERSION to 1.6.0-beta1 (JuliaLang#39120)

 Set VERSION to 1.5.3 (JuliaLang#38345)

Set VERSION to 1.5.2 (JuliaLang#37718)

Set VERSION to 1.5.1 (JuliaLang#37194)