Add Box2D for LunarLander-v2 exercise solution in chapter 18

environment.yml

@@ -4,6 +4,7 @@ channels:
   - defaults
 dependencies:
   - atari_py=0.2 # used only in chapter 18
+  - box2d-py=2.3 # used only in chapter 18
   - ftfy=5.8 # used only in chapter 16 by the transformers library
   - graphviz # used only in chapter 6 for dot files
   - gym=0.18 # used only in chapter 18

requirements.txt

@@ -49,7 +49,7 @@ tensorflow-addons==0.12.1
 
 # There are a few dependencies you need to install first, check out:
 # https://github.com/openai/gym#installing-everything
-gym[atari]==0.18.0
+gym[atari,Box2D]==0.18.0
 # On Windows, install atari_py using:
 # pip install --no-index -f https://github.com/Kojoley/atari-py/releases atari_py