Don't test that Pkg exports add

[martinholters]

Pkg3 still defines add, but doesn't export it anymore.

Minor follow-up to #551.

[martinholters]

Remaining test failures are due to JuliaLang/julia#27212. What do we do with those? CC @Sacha0

[fredrikekre]

What is the failure?

[martinholters]

ERROR: LoadError: WARNING: Base.qr is deprecated: it has been moved to the standard library package `LinearAlgebra`.
Add `using LinearAlgebra` to your imports.
 in module Base
MethodError: no method matching qr(::Array{Int64,2}, ::Val{false}; full=false)
Closest candidates are:
  qr(::AbstractArray{T,2}, ::Any) where T at usr/share/julia/stdlib/v0.7/LinearAlgebra/src/qr.jl:335 got unsupported keyword argument "full"
  qr(::AbstractArray{T,2}) where T at usr/share/julia/stdlib/v0.7/LinearAlgebra/src/qr.jl:340 got unsupported keyword argument "full"
Stacktrace:
 [1] top-level scope at Compat/test/runtests.jl:1677

It's the diappearance of the full keyword.

[fredrikekre]

Perhaps we can just version that test then.

[martinholters]

Sure, we could do that to get the tests pass. But providing this qr method on 0.6 only is of little use. It won't help with the migration to 0.7 at all. Ideally, we should probably deprecate the full keyword to ... and this is where it gets tricky. I'll open an issue (EDIT: #556) for the discussion, it doesn't really belong here.