Update to LQOI 0.6

[ianfiske]

Without this update, we can't grab the latest Cbc.jl (tagged) and Gurobi.jl (#master) due to conflicts:

(jtestenv) pkg> st
    Status `~/jtestenv/Project.toml`
  [9961bab8] Cbc v0.4.3
  [e2554f3b] Clp v0.6.0
  [2e9cd046] Gurobi v0.5.7

(jtestenv) pkg> add Cbc@0.5.0
 Resolving package versions...
ERROR: Unsatisfiable requirements detected for package LinQuadOptInterface [f8899e07]:
 LinQuadOptInterface [f8899e07] log:
 ├─possible versions are: [0.1.0, 0.2.0, 0.3.0-0.3.1, 0.4.0-0.4.3, 0.5.0, 0.6.0] or uninstalled
 ├─restricted by julia compatibility requirements to versions: [0.3.0-0.3.1, 0.4.0-0.4.3, 0.5.0, 0.6.0] or uninstalled
 ├─restricted by compatibility requirements with Clp [e2554f3b] to versions: 0.4.0-0.4.3
 │ └─Clp [e2554f3b] log:
 │   ├─possible versions are: [0.0.5-0.0.10, 0.1.0-0.1.1, 0.2.0-0.2.2, 0.3.0-0.3.1, 0.4.0, 0.5.0-0.5.1, 0.6.0] or uninstalled
 │   └─restricted to versions 0.6.0 by an explicit requirement, leaving only versions 0.6.0
 └─restricted by compatibility requirements with MathOptInterface [b8f27783] to versions: 0.6.0 or uninstalled — no versions left
   └─MathOptInterface [b8f27783] log:
     ├─possible versions are: [0.1.0, 0.2.0, 0.3.0, 0.4.0-0.4.1, 0.5.0-0.5.1, 0.6.0-0.6.4, 0.7.0, 0.8.0] or uninstalled
     ├─restricted by julia compatibility requirements to versions: [0.5.0-0.5.1, 0.6.0-0.6.4, 0.7.0, 0.8.0] or uninstalled
     └─restricted by compatibility requirements with Cbc [9961bab8] to versions: 0.8.0
       └─Cbc [9961bab8] log:
         ├─possible versions are: [0.0.5-0.0.8, 0.1.0-0.1.8, 0.2.0-0.2.5, 0.3.0-0.3.2, 0.4.0-0.4.4, 0.5.0] or uninstalled
         └─restricted to versions 0.5.0 by an explicit requirement, leaving only versions 0.5.0

[mlubin]

Closed by #50