chore: fix description content type (#34)

Author: jsstevenson

setup.cfg

@@ -2,7 +2,7 @@
 name = oxley
 description = Dynamically generate pydantic classes from JSONschema at runtime
 long_description = file: README.md, LICENSE
-long_description_content_type='text/markdown'
+long_description_content_type = text/markdown
 
 url = https://github.com/jsstevenson/oxley
 download_url = https://github.com/jsstevenson/oxley/releases