Merge pull request #228 from JohanMabille/ci

Upgraded to Xenial

Author: JohanMabille

.travis.yml

@@ -1,5 +1,5 @@
 language: cpp
-dist: trusty
+dist: xenial
 matrix:
   include:
     - os: linux
@@ -56,7 +56,7 @@ matrix:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-trusty-3.9
+            - llvm-toolchain-xenial-3.9
           packages:
             - g++-4.9
             - clang-3.9
@@ -66,7 +66,7 @@ matrix:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-trusty-4.0
+            - llvm-toolchain-xenial-4.0
           packages:
             - g++-4.9
             - clang-4.0
@@ -76,7 +76,7 @@ matrix:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-trusty-5.0
+            - llvm-toolchain-xenial-5.0
           packages:
             - g++-4.9
             - clang-5.0
@@ -86,7 +86,7 @@ matrix:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-trusty-6.0
+            - llvm-toolchain-xenial-6.0
           packages:
             - clang-6.0
       env: COMPILER=clang CLANG=6.0 PY=3