Fix isdominated in exact.jl bounds definition

[trigaut]

I think there must be a mistake in the function isdominated in exact.jl.
It was changed to transition from MathProgBase.linprog to JuMP + MOI.

The user has to define bounds lb and ub as vectors whose size are not size(A,2) but size(A,2)+1.
Two variables lbx and ubx, are defined to avoid that, but they were not properly used.

All tests pass with this fix !

[frapac]

Thank for the contribution!
Is it possible to add a unit-test in test/exact.jl to test properly the function exactpruning! when we set explicitly a lower-bound and an upper-bound?

[trigaut]

working on it !

[trigaut]

I made tests and changed the fix