Fix getAliases method output type declarations in documentation

Author: mcg-web

docs/definitions/mutation.md

@@ -75,7 +75,7 @@ class ShipMutation implements MutationInterface, AliasedInterface
     /**
      * {@inheritdoc}
      */
-    public static function getAliases()
+    public static function getAliases(): array
     {
         return [
             // `create_ship` is the name of the mutation that you SHOULD use inside of your types definition

docs/definitions/resolver.md

@@ -48,7 +48,7 @@ class Greetings implements ResolverInterface, AliasedInterface
     /**
      * {@inheritdoc}
      */
-    public static function getAliases()
+    public static function getAliases(): array
     {
         return ['sayHello' => 'say_hello'];
     }
@@ -162,7 +162,7 @@ class CalcMutation implements MutationInterface, AliasedInterface
     /**
      * {@inheritdoc}
      */
-    public static function getAliases()
+    public static function getAliases(): array
     {
         return ['addition' => 'add'];
     }

docs/definitions/type-system/index.md

@@ -60,7 +60,7 @@ Types can be define 3 different ways:
         /**
          * {@inheritdoc}
          */
-        public static function getAliases()
+        public static function getAliases(): array
         {
             return ['DateTime', 'Date'];
         }