Make travis pass on Symfony 2.2

Make travis actually update the lock file and install the 2.2 components.
Document deprecation of getClassMetadata in validator docs.

.travis.yml

@@ -6,7 +6,7 @@ env:
 
 before_script:
     # symfony/*
-    - sh -c "if [ '$SYMFONY_DEPS_VERSION' = '2.2' ]; then sed -i 's/>=2.1,<2.3-dev/2.2.*@dev/g' composer.json; fi"
+    - sh -c "if [ '$SYMFONY_DEPS_VERSION' = '2.2' ]; then sed -i 's/>=2.1,<2.3-dev/2.2.*@dev/g' composer.json; composer update --dev --prefer-source; fi"
     - composer install --dev --prefer-source
 
 php:

doc/providers/validator.rst

@@ -150,6 +150,11 @@ the class properties and getters, and then call the ``validate`` method::
         echo 'The author is valid';
     }
 
+.. note::
+
+    If you are using Symfony 2.2, replace the ``getClassMetadata`` calls with
+    calls to the new ``getMetadataFor`` method.
+
 You can also declare the class constraint by adding a static
 ``loadValidatorMetadata`` method to your classes::