Setup gurobi cloud could not be loaded

**Describe the bug**
A clear and concise description of what the bug is.

**To Reproduce**
I'm trying to run with gurobi cloud and I have been following the linux install guide for it here: https://www.gurobi.com/documentation/9.1/quickstart_linux/software_installation_guid.html

I have run a hello world with gurobipy:
```

from gurobipy import *
model = Model("hello")
x = model.addVar(obj=3000, vtype="C", name="x")
y = model.addVar(obj=4000, vtype="C", name="y")
model.update()
L1 = LinExpr([5,6],[x,y])
model.addConstr(L1,">",10)
L2 = LinExpr([7,5],[x,y])
model.addConstr(L2,">",5)
model.ModelSense = 1 # minimize
model.optimize()
```
But when I run with python mip it does not work.
I have specified my license file and gurobi home correctly

```
from mip import Model, xsum, maximize, BINARY, GRB

p = [10, 13, 18, 31, 7, 15]
w = [11, 15, 20, 35, 10, 33]
c, I = 47, range(len(w))

m = Model("knapsack", solver_name=GRB)

x = [m.add_var(var_type=BINARY) for i in I]

m.objective = maximize(xsum(p[i] * x[i] for i in I))

m += xsum(w[i] * x[i] for i in I) <= c

m.optimize()

selected = [i for i in I if x[i].x >= 0.99]
print("selected items: {}".format(selected))
```
I get:
"Gurobi environment could not be loaded, check your license."

**Expected behavior**
I expect the gurobi cloud to work after specifing the license file

**Desktop (please complete the following information):**
- Linux ubuntu docker
- 3.6.8
- Python-MIP version: 1.13

I hope you can help be

Start with the Model("knapsack", solver_name=GRB) entry point and reproduce the failure in the reported Ubuntu Docker and Python 3.6.8 environment. Compare Python-MIP's Gurobi environment setup with the direct gurobipy example and verify the configured license file and GUROBI_HOME; done means the cloud-backed model loads and the knapsack example optimizes without the environment error.

Written by the indexing model from the issue text.