Fix flake8 whitespace errors in helpers.py

- Removed trailing whitespace from blank lines (W293)
- All flake8 checks now pass

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

wikijs/utils/helpers.py

@@ -48,11 +48,11 @@ def validate_url(url: str) -> bool:
         # Check basic components exist
         if not all([result.scheme, result.netloc]):
             return False
-        
+
         # Check for invalid characters (spaces, etc.)
         if " " in url:
             return False
-            
+
         return True
     except Exception:
         return False