Fix R.21 warning to cover all Shared_pointer parameters

Closes #2226

Author: hsutter

CppCoreGuidelines.md

@@ -9879,7 +9879,7 @@ This is more efficient:
 
 ##### Enforcement
 
-(Simple) Warn if a function uses a `Shared_pointer` with an object allocated within the function, but never returns the `Shared_pointer` or passes it to a function requiring a `Shared_pointer&`. Suggest using `unique_ptr` instead.
+(Simple) Warn if a function uses a `Shared_pointer` with an object allocated within the function, but never returns the `Shared_pointer` or passes it to a function requiring a `Shared_pointer`. Suggest using `unique_ptr` instead.
 
 ### <a name="Rr-make_shared"></a>R.22: Use `make_shared()` to make `shared_ptr`s