Update linearized models for Julia 1.0

[notZaki]

This PR updates the linearized models which were still using some of the older syntax.

The script in ./test/linearTests.jl can be used to verify that the models work.
These tests were never part of the main testing suite, but I suppose they could be added by appending

@testset "Linearized models" begin
  include(joinpath(@__DIR__, "linearTests.jl"))
end

to ./test/runtests.jl.