fix(urls): parse hyphens in agency slug paths

TransitAgency.slug is a SlugField and so allows configuring an agency
with hyphens in its slug, e.g. simi-valley-transit

however the URL path parsing in TransitAgencyPathConverter failed to
account for hyphens, leading to an error for agencies so configured, e.g.

> Reverse for 'agency_index' with arguments '('simi-valley-transit',)' not found.
> 1 pattern(s) tried: ['(?P<agency>[a-zA-Z]{3,})\\Z']

Author: thekaveman

benefits/core/urls.py

@@ -26,7 +26,7 @@ class TransitAgencyPathConverter:
     """Path converter to parse valid TransitAgency objects from URL paths."""
 
     # used to test the url fragment, determines if this PathConverter is used
-    regex = "[a-zA-Z]{3,}"
+    regex = "[a-zA-Z-]{3,}"
 
     def to_python(self, value):
         """Determine if the matched fragment corresponds to an active Agency."""