add tests on bionic beaver

.travis.yml

@@ -1,7 +1,9 @@
 language: cpp
 matrix:
-# gcc
   include:
+# gcc
+#   xenial
+#   gcc 5 is the default on xenial
     - os: linux
       dist: xenial
       compiler: gcc
@@ -12,49 +14,69 @@ matrix:
             - cppcheck
             - doxygen
       env: CHECK="true"
+#   bionic
     - os: linux
-      dist: xenial
-      compiler: gcc
-    - os: linux
-      dist: xenial
+      dist: bionic
       compiler: gcc
       env: MATRIX_EVAL="CC=gcc-6 && CXX=g++-6"
+    
+    # gcc 7 is the default on bionic
     - os: linux
-      dist: xenial
+      dist: bionic
       compiler: gcc
-      env: MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
+      addons:
+        apt:
+          packages:
+            - valgrind
+            - cppcheck
+            - doxygen
+      env: CHECK="true"
     - os: linux
-      dist: xenial
+      dist: bionic
       compiler: gcc
       env: MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
 
-# clang
+# clang      
+#   xenial
+#   The default clang on xenial is clang 7.0
     - os: linux
       dist: xenial
       compiler: clang
+      addons:
+        apt:
+          packages:
+            - clang-6.0
+            - cppcheck
+            - doxygen
+      env: CHECK="true"
+
+#   bionic
+    - os: linux
+      dist: bionic
+      compiler: clang
       addons:
         apt:
           sources:
-            - llvm-toolchain-xenial-5.0
+            - llvm-toolchain-bionic-5.0
           packages:
             - clang-5.0
       env: MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0"
     - os: linux
-      dist: xenial
+      dist: bionic
+      compiler: clang
+      env: MATRIX_EVAL="CC=clang-6.0 && CXX=clang++-6.0" 
+    
+    # The default clang on bionic is clang 7.0
+    - os: linux
+      dist: bionic
       compiler: clang
       addons:
         apt:
-          sources:
-            - llvm-toolchain-xenial-6.0
           packages:
             - clang-6.0
             - cppcheck
             - doxygen
-      env: MATRIX_EVAL="CC=clang-6.0 && CXX=clang++-6.0" CHECK="true"
-    # The default clang on xenial is clang 7.0
-    - os: linux
-      dist: xenial
-      compiler: clang
+      env: CHECK="true"
 # osx
     - os: osx
       osx_image: xcode9.4
@@ -77,9 +99,6 @@ before_install:
   - if [ "$TRAVIS_OS_NAME" = "linux" ]; then
       eval "${MATRIX_EVAL}";
       if [ -n "$MATRIX_EVAL" ] && [ "$TRAVIS_COMPILER" != "clang" ]; then
-        sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6B05F25D762E3157;
-        sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test;
-        sudo apt-get update -qq;
         sudo apt-get install -y $CC;
       fi;
     fi