update ci

.travis.yml

@@ -33,6 +33,12 @@ matrix:
 
     - os: linux
       compiler: g++
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-9
       env:
         - CXX_COMPILER=g++-9 CC_COMPILER=gcc-9
 
@@ -96,12 +102,6 @@ matrix:
       env:
         - CXX_COMPILER=clang++ CC_COMPILER=clang
 
-  allow_failures: # gcc-9 yeat unstable.
-    - os: linux
-      compiler: g++
-      env:
-        - CXX_COMPILER=g++-9 CC_COMPILER=gcc-9
-
 install:
   - export CC=${CC_COMPILER}
   - export CXX=${CXX_COMPILER}
@@ -136,15 +136,6 @@ install:
       export LD_LIBRARY_PATH="${LD_LIBRARY_PATH}:${LLVM_INSTALL}/lib"
     fi
   - |
-    # If linux and gcc-9 install gcc-9.
-    if [[ "${CXX}" == "g++-9" ]]; then
-      wget http://kayari.org/gcc-latest/gcc-latest.deb
-      sudo dpkg -i gcc-latest.deb
-      sudo ln -s /opt/gcc-latest/bin/gcc /usr/bin/gcc-9
-      sudo ln -s /opt/gcc-latest/bin/g++ /usr/bin/g++-9
-      sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 90 --slave /usr/bin/g++ g++ /usr/bin/g++-9
-      sudo ldconfig /opt/gcc-latest/lib64
-    fi
 
 before_script:
   - rm -rf build