Fix importlib-metadata on Python 3.8 + bump ale-py (#2428)

* Bump ale-py -> 0.7.1

* env-plugins: parse module,attr for Python 3.8

gym/envs/registration.py

@@ -248,18 +248,28 @@ def namespace(ns):
 def load_env_plugins(entry_point="gym.envs"):
     # Load third-party environments
     for plugin in metadata.entry_points().get(entry_point, []):
-        if plugin.attr is None:
+        # Python 3.8 doesn't support plugin.module, plugin.attr
+        # So we'll have to try and parse this ourselves
+        try:
+            module, attr = plugin.module, plugin.attr
+        except AttributeError:
+            if ":" in plugin.value:
+                module, attr = plugin.value.split(":", maxsplit=1)
+            else:
+                module, attr = plugin.value, None
+        finally:
+            if attr is None:
                 raise error.Error(
-                f"Gym environment plugin `{plugin.module}` must specify a function to execute, not a root module"
+                    f"Gym environment plugin `{module}` must specify a function to execute, not a root module"
                 )
 
         context = namespace(plugin.name)
         if plugin.name == "__internal__":
-            if plugin.module in plugin_internal_whitelist:
+            if module in plugin_internal_whitelist:
                 context = contextlib.nullcontext()
             else:
                 logger.warn(
-                    f"Trying to register an internal environment when `{plugin.module}` is not in the whitelist"
+                    f"Trying to register an internal environment when `{module}` is not in the whitelist"
                 )
 
         with context:

setup.py

@@ -10,7 +10,7 @@ from version import VERSION
 
 # Environment-specific dependencies.
 extras = {
-    "atari": ["ale-py~=0.7"],
+    "atari": ["ale-py~=0.7.1"],
     "accept-rom-license": ["autorom[accept-rom-license]~=0.4.2"],
     "box2d": ["box2d-py==2.3.5", "pyglet>=1.4.0"],
     "classic_control": ["pyglet>=1.4.0"],