Removed old ppa for clang 5 and up

Author: gracicot

.travis.yml

@@ -36,11 +36,10 @@ matrix:
       addons: { apt: { packages: ["clang-4.0"], sources: ["llvm-toolchain-trusty-4.0", "ubuntu-toolchain-r-test"] } }
 
     - os: linux
-      dist: trusty
       env:
         - LLVM_VERSION=5.0.0
         - ENABLE_CXX17=true
-      addons: { apt: { packages: ["clang-5.0"], sources: ["llvm-toolchain-trusty-5.0", "ubuntu-toolchain-r-test"] } }
+      addons: { apt: { packages: ["clang-5.0"], sources: ["ubuntu-toolchain-r-test"] } }
 
     - os: linux
       env: