Fix some issues in metamaze environment

[neverparadise]

I found some errors in the metamaze environment and fixed that errors.

1. Update setup.py for including img directory in metamaze/envs
2. Fix view_grid issue for executing environment.

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[WorldEditors]

Hi, neverparadise,

• Update setup.py for including img directory in metamaze/envs Thanks for pointing out

• Fix view_grid issue for executing environment. I see you included "view_grid" as a task configuration. However, this is probably not quite what we want in meta-learning. The "view_grid" hyper-parameter can change the observation space (e.g., from 3x3 to 5x5, to 7x7 ... ). In most settings, we want different mazes, different goals as different tasks, but the view_grid should not be changed frequently. Or else, the model have to deal with different input spaces. I suggest that you double check this part. We can discuss if you have different opinions.