Fix for unknown VERSION_ID which is now a fatal error in python
3.7. Backported from upstream 638c7c7a22156ca7e542725d32dbbc71f2f008a9

--- a/Nagstamon/Helpers.py.~1~	2020-01-24 16:12:12.000000000 +0100
+++ b/Nagstamon/Helpers.py	2020-08-29 07:39:26.999988228 +0200
@@ -454,7 +454,7 @@
             for property in os_release_file.read_text().splitlines():
                 key, value = property.split('=', 1)
                 os_release_dict[key] = value.strip('"').strip("'")
-            return (os_release_dict['ID'], os_release_dict['VERSION_ID'], os_release_dict['NAME'])
+            return (os_release_dict['ID'], os_release_dict.get('VERSION_ID', 'unknown'), os_release_dict['NAME'])
         else:
             return False
     else: