(Temporarily) don't download clang package

Reviewed-by: NEmilia Käsper <emilia@openssl.org>

.travis.yml

@@ -5,13 +5,11 @@ addons:
     apt:
         packages:
             - ccache
-            - clang-3.6
             - gcc-5
             - binutils-mingw-w64
             - gcc-mingw-w64
             - wine
         sources:
-            - llvm-toolchain-precise-3.6
             - ubuntu-toolchain-r-test
 
 os:
@@ -32,10 +30,10 @@ env:
 matrix:
     include:
         - os: linux
-          compiler: clang-3.6
+          compiler: clang
           env: CONFIG_OPTS="no-shared enable-asan"
         - os: linux
-          compiler: clang-3.6
+          compiler: gcc-5
           env: CONFIG_OPTS="no-asm enable-ubsan enable-rc5 enable-md2 -fno-sanitize=alignment"
         - os: linux
           compiler: gcc-5