Allow for alias of classifier in setup.cfg

This change allows a setup.cfg file to define classifiers using
the attribute of "classifier" in addition to "classifiers". The
attribute "classifier" is an alias of "classifiers" according
to the setuptools documentation.

Fixes: #105

Signed-off-by: Eric Brown <eric_wade_brown@yahoo.com>

Author: ericwb

licensecheck/packageinfo.py

@@ -156,7 +156,10 @@ def getMyPackageMetadata() -> dict[str, Any]:
 		config = configparser.ConfigParser()
 		config.read("setup.cfg")
 		if "metadata" in config.sections() and "license" in config["metadata"]:
-			classifiers = config.get("metadata", "classifiers").strip().splitlines()
+			if "classifier" in config["metadata"]:
+				classifiers = config.get("metadata", "classifier").strip().splitlines()
+			else:
+				classifiers = config.get("metadata", "classifiers").strip().splitlines()
 			licenseStr = ucstr(config.get("metadata", "license"))
 			return {"classifiers": classifiers, "license": licenseStr}