Travis CI gcc version

.travis.yml

@@ -2,6 +2,20 @@ language: cpp
 sudo: required
 os: linux
 dist: trusty
+matrix:
+  include:
+    # works on Precise and Trusty
+    - os: linux
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-7
+      env:
+         - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
+before_install:
+    - eval "${MATRIX_EVAL}"         
 compiler:
   - clang
   - gcc