travis: fix llvm apt package names

ci/travis_linux_install

@@ -4,4 +4,4 @@ set -x
 
 sudo apt-get remove -y llvm-*
 sudo rm -rf /usr/local/*
-sudo apt-get install -y clang-7.0 libclang-7.0 libclang-7.0-dev llvm-7.0 llvm-7.0-dev liblld-7.0 liblld-7.0-dev cmake s3cmd
+sudo apt-get install -y clang-7 libclang-7-dev llvm-7 llvm-7-dev cmake s3cmd

ci/travis_linux_script

@@ -3,8 +3,8 @@
 set -x
 set -e
 
-export CC=clang-7.0
-export CXX=clang++-7.0
+export CC=clang-7
+export CXX=clang++-7
 echo $PATH
 mkdir build
 cd build