Merge pull request #1214 from est77/est_travis_gcc6

Add gcc 6 C++11 to travis builds, remove gcc 4.6.

Author: dictoon

.travis.yml

@@ -15,6 +15,8 @@ addons:
       - g++-4.8
       - gcc-5
       - g++-5
+      - gcc-6
+      - g++-6
 
 before_install:
   - git clone https://github.com/appleseedhq/travis-linux-deps.git
@@ -31,10 +33,6 @@ env:
 
 matrix:
     include:
-        - os: linux
-          compiler: gcc
-          env: GCC_VERSION= USE_CPP11=OFF
-
         - os: linux
           compiler: gcc
           env: GCC_VERSION=5 USE_CPP11=OFF
@@ -47,6 +45,10 @@ matrix:
           compiler: gcc
           env: GCC_VERSION=5 USE_CPP11=ON
 
+        - os: linux
+          compiler: gcc
+          env: GCC_VERSION=6 USE_CPP11=ON
+
 script:
   - ./travis/build.sh