add release date for 0.5.1
add release date for 0.5.1

JuliaCI/PackageEvaluator.jl,ScottPJones/PackageEvaluator.jl,IainNZ/PackageEvaluator.jl,ScottPJones/PackageEvaluator.jl,IainNZ/PackageEvaluator.jl,JuliaCI/PackageEvaluator.jl,ScottPJones/PackageEvaluator.jl,JuliaCI/PackageEvaluator.jl,IainNZ/PackageEvaluator.jl