typo

README.md

@@ -10,7 +10,7 @@ Gym currently has two pieces of documentation: the [documentation website](http:
 
 To install the base Gym library, use `pip install gym`.
 
-This does not include dependencies for all families of environments (there's a massive number, and some can be problematic to install on certain systems). You can install these dependencies for one family like `pip install gym[atari]` or use `pip install gym[box2d]` to install all dependencies.
+This does not include dependencies for all families of environments (there's a massive number, and some can be problematic to install on certain systems). You can install these dependencies for one family like `pip install gym[atari]` or use `pip install gym[all]` to install all dependencies.
 
 We support Python 3.6, 3.7, 3.8 and 3.9 on Linux and macOS. We will accept PRs related to Windows, but do not officially support it.