Merge branch '3.4' into 4.1

* 3.4:
  Use the real image URL for the filesystem tests
  [Finder] Update PHPdoc append()
  [DI] Fix phpdoc
  Fix code examples in PHPDoc
  [HttpKernel] Fix inheritdocs
  bumped Symfony version to 3.4.16
  updated VERSION for 3.4.15
  updated CHANGELOG for 3.4.15

Author: sroze

ConstraintViolationInterface.php

@@ -19,11 +19,9 @@
  * element in the validation graph and the root element that was originally
  * passed to the validator. For example, take the following graph:
  *
- * <pre>
- * (Person)---(firstName: string)
- *      \
- *   (address: Address)---(street: string)
- * </pre>
+ *     (Person)---(firstName: string)
+ *          \
+ *       (address: Address)---(street: string)
  *
  * If the <tt>Person</tt> object is validated and validation fails for the
  * "firstName" property, the generated violation has the <tt>Person</tt>