#1165 - Use size of m for return type

[mforets]

Closes #1165.

[mforets]

This gives:

julia> using LazySets
[ Info: Recompiling stale cache file /Users/forets/.julia/compiled/v1.1/LazySets/NjrGc.ji for LazySets [b4f0291d-fe17-52bc-9479-3d1a343d9043]

julia> H, M = rand(Hyperrectangle, dim=2), rand(1, 2)
(Hyperrectangle{Float64}([0.392449, 2.20354], [0.242798, 0.00991168]), [0.613442 0.725116])

julia> MH = linear_map(M, H, use_inv=false)
Interval{Float64,IntervalArithmetic.Interval{Float64}}([1.68243, 1.9947])

julia> MH = linear_map(M, H)
Interval{Float64,IntervalArithmetic.Interval{Float64}}([1.68243, 1.9947])