E.18: fix grammar (#1481)

CppCoreGuidelines.md

@@ -15727,7 +15727,7 @@ Let cleanup actions on the unwinding path be handled by [RAII](#Re-raii).
 
 ##### Reason
 
- `try`/`catch` is verbose and non-trivial uses error-prone.
+ `try`/`catch` is verbose and non-trivial uses are error-prone.
  `try`/`catch` can be a sign of unsystematic and/or low-level resource management or error handling.
 
 ##### Example, Bad