Update CI to use Ubuntu Xenial and test with g++ 8

Author: Crayon2000

.travis.yml

@@ -2,7 +2,7 @@ language: cpp
 matrix:
   include:
 #  - os: linux
-#    dist: trusty
+#    dist: xenial
 #    compiler: clang
 #    before_install:
 #    - sudo add-apt-repository ppa:kubuntu-ppa/backports -y
@@ -19,7 +19,7 @@ matrix:
 #    - g++ -v
 
   - os: linux
-    dist: trusty
+    dist: xenial
     compiler: gcc
     env:
       - COMPILER=g++-4.8
@@ -28,7 +28,7 @@ matrix:
         sources: ['ubuntu-toolchain-r-test']
         packages: [g++-4.8, valgrind]
   - os: linux
-    dist: trusty
+    dist: xenial
     compiler: gcc
     env:
       - COMPILER=g++-4.9
@@ -37,7 +37,7 @@ matrix:
         sources: ['ubuntu-toolchain-r-test']
         packages: [g++-4.9, valgrind]
   - os: linux
-    dist: trusty
+    dist: xenial
     compiler: gcc
     env:
       - COMPILER=g++-5
@@ -46,7 +46,7 @@ matrix:
         sources: ['ubuntu-toolchain-r-test']
         packages: [g++-5, valgrind]
   - os: linux
-    dist: trusty
+    dist: xenial
     compiler: gcc
     env:
       - COMPILER=g++-6
@@ -55,14 +55,23 @@ matrix:
         sources: ['ubuntu-toolchain-r-test']
         packages: [g++-6, valgrind]
   - os: linux
-    dist: trusty
+    dist: xenial
     compiler: gcc
     env:
       - COMPILER=g++-7
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
         packages: [g++-7, valgrind]
+  - os: linux
+    dist: xenial
+    compiler: gcc
+    env:
+      - COMPILER=g++-8
+    addons:
+      apt:
+        sources: ['ubuntu-toolchain-r-test']
+        packages: [g++-8, valgrind]
 
 before_install:
  - sudo apt-get -qq update