Query.Dependencies now retrurns a tuple

Fix `Pkg.Entry.check_metatdata` due to api changes in  https://github.com/JuliaLang/julia/commit/69f930e6c01d6ff049dd100cf12ca0ec7fd4aa41

This in turn is causing the METADATA.jl travis tests to fail. https://travis-ci.org/JuliaLang/METADATA.jl/builds/12866672