Correct setup scripts for MuJoCo 2.0

[ryanjulian]

MuJoCo changed their naming convention for versions inside .mujoco, but
I didn't catch this in #494

[codecov]

Codecov Report

Merging #498 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #498      +/-   ##
==========================================
+ Coverage   63.12%   63.19%   +0.07%     
==========================================
  Files         186      186              
  Lines       12159    12159              
==========================================
+ Hits         7675     7684       +9     
+ Misses       4484     4475       -9

Impacted Files	Coverage Δ
garage/envs/mujoco/gather/gather_env.py	56.56% <0%> (+0.33%)	⬆️
garage/envs/mujoco/maze/maze_env.py	82.21% <0%> (+1.44%)	⬆️
garage/envs/mujoco/point_env.py	77.77% <0%> (+11.11%)	⬆️

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[coveralls]

Coverage decreased (-0.02%) to 63.302% when pulling e40d56c on mjpro200 into 4ff4a20 on master.