update version of clang-format on Travis CI

Author: rhysd

.travis.yml

@@ -2,8 +2,8 @@ language: ruby
 rvm:
     - 1.9.3
 env:
-    - CLANG_VERSION="3.7"
-    - CLANG_VERSION="3.8"
+    - CLANG_VERSION="4.0"
+    - CLANG_VERSION="5.0"
 
 install:
     - bundle install
@@ -15,10 +15,10 @@ script:
 addons:
     apt:
         sources:
-            - llvm-toolchain-precise-3.8
-            - llvm-toolchain-precise-3.7
+            - llvm-toolchain-precise-5.0
+            - llvm-toolchain-precise-4.0
             - ubuntu-toolchain-r-test
         packages:
             - g++-4.9
-            - clang-format-3.7
-            - clang-format-3.8
+            - clang-format-5.0
+            - clang-format-4.0