Update dependencies for 1.0 compatibility.

[englhardt]

Installing MLKernels on Julia 1.0 currently fails due to a dependency issue.

(v1.0) pkg> add MLKernels
  Updating registry at `~/.julia/registries/General`
  Updating git-repo `https://github.com/JuliaRegistries/General.git`
 Resolving package versions...
ERROR: Unsatisfiable requirements detected for package MLKernels [6899632a]:
 MLKernels [6899632a] log:
 ├─possible versions are: [0.0.1-0.0.3, 0.1.0, 0.2.0, 0.3.0] or uninstalled
 ├─restricted to versions * by an explicit requirement, leaving only versions [0.0.1-0.0.3, 0.1.0, 0.2.0, 0.3.0]
 └─restricted by julia compatibility requirements to versions: uninstalled — no versions left

With the newest release of SpecialFunctions.jl (JuliaLang/METADATA.jl#19167) we can now update the dependencies of MLKernels.jl. This enables full compatibility for Julia 1.0 (CI passes).

Please trigger a new release on METADATA.jl after merging this to allow users to finally use this great package with Julia 1.0.

A test coverage drop may occur, see the bug and discussion here: JuliaLang/julia#28192.

[trthatcher]

Thanks for doing this.

I'll tag a new release on METADATA.jl in the next day or so.