Ember Data: further fix Snapshot.belongsTo, Snapshot.attr.

# Conflicts:
#	types/ember-data/index.d.ts

types/ember-data/index.d.ts

@@ -942,7 +942,7 @@ declare module 'ember-data' {
             /**
              * Returns the value of an attribute.
              */
-            attr<L extends keyof ModelRegistry[K]>(keyName: L): {};
+            attr<L extends keyof ModelRegistry[K]>(keyName: L): ModelRegistry[K][L];
             /**
              * Returns all attributes and their corresponding values.
              */
@@ -957,7 +957,7 @@ declare module 'ember-data' {
             belongsTo<L extends keyof ModelRegistry & keyof ModelRegistry[K]>(
                 keyName: L,
                 options?: {}
-            ): Snapshot<L> | string | null | undefined;
+            ): Snapshot<K>['record'][L] | string | null | undefined;
             /**
              * Returns the current value of a hasMany relationship.
              */

types/ember-data/tsconfig.json

@@ -34,4 +34,4 @@
         "test/injections.ts",
         "test/error.ts"
     ]
-}
+}