Update standard/interfaces.md

Fixes typo

Co-authored-by: Bill Wagner <[email protected]>

Author: 2 people

standard/interfaces.md

@@ -659,7 +659,7 @@ It is not possible to access an explicit interface member implementation through
 
 It is a compile-time error for an explicit interface member implementation to include any modifiers ([§15.6](classes.md#156-methods)) other than `extern` or `async`.
 
-If *type_parameter_constraints_clause*s are present in an explicit interface method implementation, each of their *type_parameter_constraints* shall be `class` or `struct`, and for the constraint `class` in the implementation shall correspond to a type parameter in the interface method that is known to be a non-nullable reference type. Any type parameter that has the `struct` constraint in the implementation shall correspond to a type parameter in the interface method that is known to be a non-nullable value type. In the absence of *type_parameter_constraints_clause*s, the constraints for an explicit interface method implementation are inherited from the interface method, and for the constraint `class` a parameter type `T?` is interpreted as `System.Nullable<T>`.
+If *type_parameter_constraints_clause*s are present in an explicit interface method implementation, each of their *type_parameter_constraints* shall be `class` or `struct`, and for the constraint `class` in the implementation shall correspond to a type parameter in the interface method that is known to be a non-nullable reference type. Any type parameter that has the `struct` constraint in the implementation shall correspond to a type parameter in the interface method that is known to be a non-nullable value type. In the absence of *type_parameter_constraints_clause*s, the constraints for an explicit interface method implementation are inherited from the interface method, and for the constraint `struct` a parameter type `T?` is interpreted as `System.Nullable<T>`.
 
 > *Example*: The following demonstrates how the rules work when type parameters are involved:
 >