Typo.

.travis.yml

@@ -49,7 +49,7 @@ before_install:
 
 before_script:
   - export PATH=$HOME/cmake-3.1.1-Linux-x86_64/bin:$PATH
-  - if [ "CC" == "gcc" ]; then export CXX=g++-4.8 CC=gcc-4.8; fi
+  - if [ "$CC" == "gcc" ]; then export CXX=g++-4.8 CC=gcc-4.8; fi
 
 script:
   - mkdir build