Updated install page to v2.4.*
Change symfony version on composer.json
some tweaks to the Expression Language cache chapter
Merge pull request #3287 from h4cc/patch-1

Updated install page to v2.4.*
Merge pull request #3298 from pauliusmasiliunas/patch-1

Change symfony version on composer.json
Merge pull request #3300 from xabbuh/expression-component-cache-tweaks

some tweaks to the Expression Language cache chapter
adding XML code block