Fix capitalization

Author: andrewdnolan

pyproject.toml

@@ -65,7 +65,7 @@ line_length = "79"
 minversion = "6"
 addopts = ["-ra", "--showlocals", "--strict-markers", "--strict-config"]
 xfail_strict = true
-filterwarnings = ["error"]
+filterwarnings = ["ERROR"]
 log_cli_level = "info"
 testpaths = ["tests"]