upgrading clang

.travis.yml

@@ -19,12 +19,12 @@ addons:
     sources:
       - ubuntu-toolchain-r-test
       - george-edison55-precise-backports
-      - llvm-toolchain-trusty-5.0
+      - llvm-toolchain-trusty-7
     packages:
       - cmake
       - cmake-data
       - g++-7
-      - clang-5.0
+      - clang-7
 
 matrix:
     exclude:
@@ -51,6 +51,8 @@ before_install:
 install:
   - if [[ "$CXX" == "g++" ]]; then export CC="gcc-7"  ;fi
   - if [[ "$CXX" == "g++" ]]; then export CXX="g++-7" ;fi
+  - if [[ "$CXX" == "clang++" && "${TRAVIS_OS_NAME}" != "osx" ]]; then export CC="clang-7"    ;fi
+  - if [[ "$CXX" == "clang++" && "${TRAVIS_OS_NAME}" != "osx" ]]; then export CXX="clang++-7" ;fi
 
 # Universal Setup
 before_script: