.travis.yml: attempt to support multiple GCC versions #4

Author: davidmalcolm

.travis.yml

@@ -54,6 +54,10 @@ matrix:
       env:
         - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
 
+language: c
+compiler:
+  - gcc
+
 before_install:
   - eval "${MATRIX_EVAL}"
   - sudo apt-get update -qq