minor symfony#18616 Fix typo in VarDumper README (WouterSioen)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes symfony#18616).

Discussion
----------

Fix typo in VarDumper README

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
-------

36e65fc Fix typo in VarDumper README

Author: nicolas-grekas

src/Symfony/Component/VarDumper/README.md

@@ -2,7 +2,7 @@ VarDumper Component
 ===================
 
 The VarDumper component provides mechanisms for walking through any arbitrary
-PHP variable. Built on top, it provides a better `dump()`` function that you
+PHP variable. Built on top, it provides a better `dump()` function that you
 can use instead of `var_dump`.
 
 Resources