Parrallel powerlines not displayed

[BDonnot]

The parrallel powelines are not displayed properly, the will overlap in the plot helper.

reproduce it:

import grid2op
env = grid2op.make("rte_case5_example", test=True)
obs = env.reset()
_ = env.render()

There are actually 2 powerlines going from substation 2 to substations 3

[Tezirg]

Fixed PlotGrid in 0.8.2