Slice to SlugField's default max_length to avoid

"value too long for type character varying(50)"
error when slug is too long.

src/sluggable/models.py

@@ -48,7 +48,7 @@ def _generate_slug(self):
             # the current value of the "slug" variable is safe to use.
             pass
 
-        return slug
+        return slug[0:50]
 
     def _generate_base_slug(self):
         """