Update .travis.yml

.travis.yml

@@ -2,7 +2,7 @@ sudo: required
 language: cpp
 matrix:
   include:
-    # works on Precise and Trusty
+
     - os: linux
       addons:
         apt:
@@ -12,11 +12,26 @@ matrix:
             - g++-6
       env:
         - MATRIX_EVAL="CC=gcc-6 && CXX=g++-6"
+    
+    - os: linux
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-7
+      env:
+        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
 
     - os: osx
       osx_image: xcode8
       env:
-        - MATRIX_EVAL="brew update && brew upgrade && brew install gcc@6 && CC=gcc-6 && CXX=g++-6"
+        - MATRIX_EVAL="brew install gcc6 && CC=gcc-6 && CXX=g++-6"
+        
+    - os: osx
+      osx_image: xcode8
+      env:
+        - MATRIX_EVAL="brew install gcc && CC=gcc-7 && CXX=g++-7"
 
 before_install:
   - eval "${MATRIX_EVAL}"