travis: remove sudo requirement in order to be able to build on faster container system

.travis.yml

@@ -1,11 +1,5 @@
 language: cpp
 
-sudo: required
-# not totally clear why this is required, but travis support recommended it
-# to allow gcc-4.8 to be installed as the system gcc
-services:
-- docker
-
 # need at least gcc 4.8 for -std=c++11
 addons:
   apt:
@@ -14,7 +8,11 @@ addons:
     packages:
     - gcc-4.8
     - g++-4.8
- 
+
+# use gcc-4.8
+install:
+- if [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi
+
 script: make
 
 compiler: