fixed docs titles

doc/providers/asset.rst

-AssetServiceProvider
-====================
+Asset
+=====
 
 The *AssetServiceProvider* provides a way to manage URL generation and
 versioning of web assets such as CSS stylesheets, JavaScript files and image

doc/providers/csrf.rst

-CsrfServiceProvider
-===================
+CSRF
+====
 
 The *CsrfServiceProvider* provides a service for building forms in your
 application with the Symfony Form component.

doc/providers/locale.rst

-LocaleServiceProvider
-=====================
+Locale
+======
 
 The *LocaleServiceProvider* manages the locale of an application.
 

doc/providers/var-dumper.rst

-VarDumperServiceProvider
-========================
+Var Dumper
+==========
 
 The *VarDumperServiceProvider* provides a mechanism that allows exploring then
 dumping any PHP variable.