Run tests on Julia 0.7, 1.0, 1.2, 1.3

[giordano]

I'm dropping Julia 1.1 as it is not supported any more, having being superseded by Julia 1.2, see https://discourse.julialang.org/t/julia-v1-2-0-has-been-released/27742

[coveralls]

Coverage decreased (-1.0%) to 91.033% when pulling fa3eeb0 on giordano:tests into 35443c2 on JuliaGraphics:master.

[lobingera]

I understand, but for packages that define infrastructure, some more should be tested.
1.2 is current -> 1.1 + 1.0
I'm wondering if 0.7 should be dropped now, as it's 'just' a variant of 1.0.

[giordano]

Ok, so drop 0.7 completely (I'm totally fine with it), and test all versions 1.0 -> 1.3 + nightly?