Add gcc-6 to .travis.yml

Alan Jeffrey · Alan Jeffrey · commit f97767d9e895 · 2019-05-03T15:50:34.000-05:00
diff --git a/.travis.yml b/.travis.yml
@@ -17,6 +17,7 @@ addons:
       - llvm-toolchain-xenial-5.0
     packages:
       - autoconf2.13
+      - gcc-6
       - g++-6
       - clang-5.0
 
