docs(authentication): fix error message text in missing key example

The comment on the print(e) line said "env var." but the actual
ValidationError raised by _client.py says "environment variable."

Author: jhamon

docs/getting-started/authentication.md

@@ -42,7 +42,7 @@ from pinecone import Pinecone, PineconeConfigurationError
 try:
     pc = Pinecone()
 except PineconeConfigurationError as e:
-    print(e)  # "No API key provided. Pass api_key='...' or set the PINECONE_API_KEY env var."
+    print(e)  # "No API key provided. Pass api_key='...' or set the PINECONE_API_KEY environment variable."
 ```
 
 ## Security best practices