fix(circle): do not specify gcc version
fix(circle): do not specify gcc version

Default gcc version on circle is now 4.9, more than enough for our
purposes.

https://discuss.circleci.com/t/container-image-update-201512-01/1206

lucisilv/Silviu_S3-Antidote,scality/S3,scality/S3,lucisilv/Silviu_S3-Antidote,lucisilv/Silviu_S3-Antidote,lucisilv/Silviu_S3-Antidote,tomateos/S3,tomateos/S3,scality/S3,tomateos/S3,truststamp/S3,truststamp/S3,scality/S3,scality/S3,truststamp/S3,tomateos/S3,tomateos/S3,lucisilv/Silviu_S3-Antidote,tomateos/S3,truststamp/S3,lucisilv/Silviu_S3-Antidote,scality/S3,lucisilv/Silviu_S3-Antidote,truststamp/S3,truststamp/S3,tomateos/S3,tomateos/S3,lucisilv/Silviu_S3-Antidote,scality/S3,scality/S3,truststamp/S3,truststamp/S3