Only display exception type if no traceback

Update test to match

qutebrowser/config/configexc.py

@@ -92,9 +92,11 @@ class ConfigErrorDesc:
     traceback = attr.ib(None)
 
     def __str__(self):
-        return '{} - {}: {} '.format(self.text,
-                                     self.exception.__class__.__name__,
-                                     self.exception)
+        if self.traceback:
+            return '{} - {}: {} '.format(self.text,
+                                         self.exception.__class__.__name__,
+                                         self.exception)
+        return '{}: {}'.format(self.text, self.exception)
 
     def with_text(self, text):
         """Get a new ConfigErrorDesc with the given text appended."""

tests/unit/config/test_configexc.py

@@ -74,7 +74,7 @@ def test_config_file_errors_str(errors):
     assert str(errors).splitlines() == [
         'Errors occurred while reading config.py:',
         '  Error text 1: Exception 1',
-        '  Error text 2: Exception 2',
+        '  Error text 2 - Exception: Exception 2 ',
     ]