Fix visualization and correct test

[cpondoc]

Fixed visualization errors. Addresses #7.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.61702% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 98.83%. Comparing base (d4281f4) to head (6f00e5d).
Report is 11 commits behind head on master.

Files	Patch %	Lines
pyrorl/pyrorl/envs/pyrorl.py	92.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
- Coverage   99.03%   98.83%   -0.21%     
==========================================
  Files           9        9              
  Lines         933      943      +10     
==========================================
+ Hits          924      932       +8     
- Misses          9       11       +2     

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[joey-obrien]

Looks good to me