Only generate coverage once

Author: xzyfer

.travis.yml

@@ -37,7 +37,7 @@ matrix:
     - os: osx
       compiler: gcc
     - os: osx
-      env: AUTOTOOLS=no COVERAGE=yes BUILD=static
+      env: AUTOTOOLS=no BUILD=static
 
 script: ./script/ci-build-libsass
 before_install: ./script/ci-install-deps