Rename metavar to clarify required usage syntax

README.md

diff --git a/README.md b/README.md
index fc574ed..43b9887 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,7 @@
 - `detect-aws-credentials` - Checks for the existence of AWS secrets that you
   have set up with the AWS CLI.
   The following arguments are available:
-  - `--credentials-file CREDENTIAL_FILES` - additional AWS CLI style
+  - `--credentials-file CREDENTIALS_FILE` - additional AWS CLI style
     configuration file in a non-standard location to fetch configured
     credentials from. Can be repeated multiple times.
   - `--allow-missing-credentials` - Allow hook to pass when no credentials are

pre_commit_hooks/detect_aws_credentials.py

diff --git a/pre_commit_hooks/detect_aws_credentials.py b/pre_commit_hooks/detect_aws_credentials.py
index 47a69bf..35638b7 100644
--- a/pre_commit_hooks/detect_aws_credentials.py
+++ b/pre_commit_hooks/detect_aws_credentials.py
@@ -87,7 +87,7 @@
     parser.add_argument('filenames', nargs='+', help='Filenames to run')
     parser.add_argument(
         '--credentials-file',
-        dest='credential_files',
+        dest='credentials_file',
         action='append',
         default=[
             '~/.aws/config', '~/.aws/credentials', '/etc/boto.cfg', '~/.boto',
@@ -105,7 +105,7 @@
     )
     args = parser.parse_args(argv)
 
-    credential_files = set(args.credential_files)
+    credential_files = set(args.credentials_file)
 
     # Add the credentials files configured via environment variables to the set
     # of files to to gather AWS secrets from.