Add missing brackets to PropertyAccessor examples

Author: loonytoons

components/property_access/introduction.rst

@@ -327,7 +327,7 @@ instead::
 
  $person = new Person();
 
- if ($accessor->isReadable($person, 'firstName') {
+ if ($accessor->isReadable($person, 'firstName')) {
  // ...
  }
 
@@ -338,7 +338,7 @@ method to find out whether a property path can be updated::
 
  $person = new Person();
 
- if ($accessor->isWritable($person, 'firstName') {
+ if ($accessor->isWritable($person, 'firstName')) {
  // ...
  }