Credentials fix (#74)

* updating grpcio dependency

* fixes credential path bug

Author: mchestnut91

btrdb/utils/credentials.py

@@ -27,7 +27,7 @@
 
 CONFIG_DIR = ".predictivegrid"
 CREDENTIALS_FILENAME = "credentials.yaml"
-CREDENTIALS_PATH = os.path.join(os.environ["HOME"], CONFIG_DIR, CREDENTIALS_FILENAME)
+CREDENTIALS_PATH = os.path.join(os.path.expanduser("~"), CONFIG_DIR, CREDENTIALS_FILENAME)
 
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