resolves userwarning pkg_resources deprecation (#273)

* resolves userwarning @272

* Update core.py

---------

Co-authored-by: Tom Kralidis <[email protected]>

Author: pvgenuchten

pygeometa/core.py

@@ -46,11 +46,11 @@
 
 from collections.abc import Mapping
 from datetime import date, datetime
+from importlib.metadata import version, PackageNotFoundError
 import json
 import logging
 import os
 import pathlib
-import pkg_resources
 import re
 from typing import IO, Union
 from xml.dom import minidom
@@ -70,7 +70,12 @@
 
 SCHEMAS = pathlib.Path(__file__).resolve().parent / 'schemas'
 
-VERSION = pkg_resources.require('pygeometa')[0].version
+try:
+    package_version = version('pygeometa')
+except PackageNotFoundError:
+    package_version = 'unknown'
+
+VERSION = package_version
 
 
 def get_charstring(option: Union[str, dict], language: str,