Use LLVM 10 on Travis CI.

PiperOrigin-RevId: 306236199

.travis.yml

@@ -20,11 +20,11 @@ env:
 addons:
   apt:
     sources:
-    - sourceline: 'deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main'
+    - sourceline: 'deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-10 main'
       key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
     - sourceline: 'ppa:ubuntu-toolchain-r/test'
     packages:
-    - clang-9
+    - clang-10
     - cmake
     - gcc-9
     - g++-9
@@ -40,7 +40,7 @@ addons:
     - gcc@9
     - gperftools
     - kyoto-cabinet
-    - llvm@9
+    - llvm@10
     - ninja
     - snappy
     - sqlite3
@@ -60,7 +60,7 @@ install:
 # below don't work on macOS. Fortunately, the path change above makes the
 # default values (clang and clang++) resolve to the correct compiler on macOS.
 - if [ "$TRAVIS_OS_NAME" = "linux" ]; then
-    if [ "$CXX" = "clang++" ]; then export CXX="clang++-9" CC="clang-9"; fi;
+    if [ "$CXX" = "clang++" ]; then export CXX="clang++-10" CC="clang-10"; fi;
   fi
 - echo ${CC}
 - echo ${CXX}