update introspection and validation

Author: mike-marcacci

spec/Section 4 -- Introspection.md

@@ -135,8 +135,6 @@ type __Type {
 
   # OBJECT and INTERFACE only
   fields(includeDeprecated: Boolean = false): [__Field!]
-
-  # OBJECT only
   interfaces: [__Type!]
 
   # INTERFACE and UNION only
@@ -284,6 +282,7 @@ Fields
 * `fields`: The set of fields required by this interface.
   * Accepts the argument `includeDeprecated` which defaults to {false}. If
     {true}, deprecated fields are also returned.
+* `interfaces`: The set of interfaces that an interface implements.
 * `possibleTypes` returns the list of types that implement this interface.
   They must be object types.
 * All other fields must return {null}.

spec/Section 5 -- Validation.md

@@ -1104,8 +1104,8 @@ fragment catInDogFragmentInvalid on Dog {
 
 ##### Abstract Spreads in Object Scope
 
-In scope of an object type, unions or interface spreads can be used
-if the object type implements the interface or is a member of the union.
+In scope of an object or interface type, unions or interface spreads can be
+used if the type implements the interface or is a member of the union.
 
 For example
 
@@ -1145,8 +1145,8 @@ declaration, not its body.
 ##### Object Spreads In Abstract Scope
 
 Union or interface spreads can be used within the context of an object type
-fragment, but only if the object type is one of the possible types of
-that interface or union.
+fragment or interface type fragment, but only if the type is one of the
+possible types of that interface or union.
 
 For example, the following fragments are valid: