fix comparison to work with 0.21

[lucaferranti]

now I get

(RangeEnclosures) pkg> st
Project RangeEnclosures v0.2.2
Status `~/.julia/dev/RangeEnclosures/Project.toml`
  [f6369f11] ForwardDiff v0.10.36
  [d1acc4aa] IntervalArithmetic v0.21.2
  [379f33d0] ReachabilityBase v0.2.0
  [ae029012] Requires v1.3.0

julia> h(x) = sin(x[1]) - cos(x[2]) - sin(x[1]) * cos(x[1])
h (generic function with 1 method)

julia> Dh = IntervalBox(-5 .. 5, -5 .. 5)
[-5.0, 5.0]²

julia> res = enclose(h, Dh, BranchAndBoundEnclosure())
[-2.71068, 2.71313]

fixes #149

[lucaferranti]

the issue was with a bug with how > and >= are defined in IA v0.21

[schillic]

Can we test this somehow?