travis: fix env

Author: proppy

.travis.yml

@@ -9,15 +9,15 @@ matrix:
         - ubuntu-toolchain-r-test
         packages:
         - g++-4.8
-    env: COMPILER=g++-4.8
+    env: CXX=g++-4.8
   - compiler: clang
     addons:
       apt:
         sources:
         - ubuntu-toolchain-r-test
         - llvm-toolchain-precise-3.8
         packages:
-        - clang-3.7
-    env: COMPILER=clang++-3.8
+        - clang-3.8
+    env: CXX=clang++-3.8
 script:
 - make -C test/modem