Update .travis.yml

.travis.yml

@@ -30,17 +30,11 @@ matrix:
       compiler: gcc
       env: BUILD_TYPE=Debug VERBOSE=1 CXX_FLAGS=-std=c++11
     - os: linux
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.7
-          packages:
-            - clang-3.7
-      env:
-        - MATRIX_EVAL="CC=clang-3.7 && CXX=clang++-3.7" BUILD_TYPE=Debug VERBOSE=1
+      group: deprecated-2017Q4
       compiler: clang
+      env: BUILD_TYPE=Debug VERBOSE=1
     - os: linux
+      group: deprecated-2017Q4
       compiler: clang
       env: BUILD_TYPE=Release VERBOSE=1 CXX_FLAGS=-std=c++11
     - os: linux