fix docs typo

Author: andrewjschuang

docs-v2/pages/environment-variables.mdx

@@ -73,7 +73,7 @@ Reference the same environment variable in Python:
 
 ```python
 import os
-print(os.environ[API_KEY])
+print(os.environ["API_KEY"])
 ```
 
 Variable names are case-sensitive. Use the key name you defined when referencing your variable in `process.env`.