Added the release dates for the upcoming Symfony 3 versions

Author: javiereguiluz

contributing/community/releases.rst

@@ -96,12 +96,16 @@ Version  Feature Freeze  Release  End of Maintenance        End of Life
 2.4      09/2013         11/2013  09/2014 (10 months [1]_)  01/2015
 2.5      02/2014         05/2014  01/2015 (8 months)        07/2015
 2.6      09/2014         11/2014  07/2015 (8 months)        01/2016
-**2.7**  02/2015         05/2015  05/2018 (36 months)       05/2019
-2.8      09/2015         11/2015  07/2016 (8 months)        01/2017
+**2.7**  02/2015         05/2015  05/2018 (36 months [2]_)  05/2019
+3.0      09/2015         11/2015  07/2016 (8 months)        01/2017
+3.1      02/2016         05/2016  01/2017 (8 months)        07/2017
+3.2      09/2016         11/2016  07/2017 (8 months)        01/2018
+**3.3**  02/2017         05/2017  05/2020 (36 months)       05/2021
 ...      ...             ...      ...                       ...
 =======  ==============  =======  ========================  ===========
 
 .. [1] Symfony 2.4 maintenance has been `extended to September 2014`_.
+.. [2] Symfony 2.7 is the last version of the Symfony 2.x branch.
 
 .. tip::