Build both gcc and clan

I am getting different errors from clang than I did locally with gcc
diff --git a/.travis.yml b/.travis.yml
index 24e8773..35b6870 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,8 +14,8 @@
   exclude:
     - compiler: gcc
       env: USE_CONTEXT=OFF
-    - compiler: gcc
-      env: USE_CONTEXT=OFF USE_EMBEDTLS=ON
+#    - compiler: gcc
+#      env: USE_CONTEXT=OFF USE_EMBEDTLS=ON
 addons:
   apt:
     sources: