Fix pretty-printing of nullable types

lib/PhpParser/PrettyPrinter/Standard.php

@@ -34,7 +34,7 @@ class Standard extends PrettyPrinterAbstract
     }
 
     protected function pNullableType(Node\NullableType $node) {
-        return '?' . $node->type;
+        return '?' . $this->pType($node->type);
     }
 
     // Names

test/PhpParser/NodeVisitor/NameResolverTest.php

@@ -244,7 +244,7 @@ function fn2(array $a) : array
 }
 function (\NS\A $a) : \NS\A {
 };
-function fn3(?NS\A $a) : ?NS\A
+function fn3(?\NS\A $a) : ?\NS\A
 {
 }
 function fn4(?array $a) : ?array

test/code/prettyPrinter/stmt/nullable_types.test

@@ -1,11 +1,11 @@
 Nullable types
 -----
 <?php
-function test(?Foo $bar, ?string $foo) : ?Baz
+function test(?Foo $bar, ?string $foo, ?\Xyz $zyx) : ?Baz
 {
 }
 -----
 !!php7
-function test(?Foo $bar, ?string $foo) : ?Baz
+function test(?Foo $bar, ?string $foo, ?\Xyz $zyx) : ?Baz
 {
 }