n_jobs deprecated in sklearn Kmeans

[Aneoshun]

Hi,

Running the cvt_rastrigin example (but I guess that's valid for any example) raises:
TypeError: KMeans.__init__() got an unexpected keyword argument 'n_jobs'

Removing this argument here solves it: https://github.com/resibots/pymap_elites/blob/master/map_elites/common.py#L194

However, I cannot find in the doc what this argument what used for, so I leave this to you @jbmouret to decide if it is safe to remove it.

Best,

[jbmouret]

It was supposed to enable parallelization of Kmeans, but apparently they removed the argument. Please make a PR without it :)