fix bug of gcc version

Author: Han Wang

.travis.yml

@@ -33,13 +33,13 @@ matrix:
       - TENSORFLOW_VERSION=1.14
     - python: 3.6
       env: 
-      - CC=gcc-5.0
-      - CXX=g++-5.0
+      - CC=gcc-5
+      - CXX=g++-5
       - TENSORFLOW_VERSION=1.14
     - python: 3.6
       env: 
-      - CC=gcc-8.0
-      - CXX=g++-8.0
+      - CC=gcc-8
+      - CXX=g++-8
       - TENSORFLOW_VERSION=1.14
     - python: 3.7
       env: