travis-ci only run make check within docker (#4854)

 * otherwise the build environment doesn't get the proper return code

.travis.yml

@@ -48,7 +48,7 @@ env:
 
 script:
   - if [ "${TRAVIS_OS_NAME}" = "linux" ]; then
-      docker run --rm -v `pwd`:`pwd`:rw -v $HOME/.ccache:$HOME/.ccache:rw -e CCACHE_DIR=$HOME/.ccache -w=`pwd` --user=$UID -it ${DOCKER_REPO} /bin/bash -c "ccache -z; make check VECTORCONTROL=1; ccache -s";
+      docker run --rm -v `pwd`:`pwd`:rw -v $HOME/.ccache:$HOME/.ccache:rw -e CCACHE_DIR=$HOME/.ccache -w=`pwd` --user=$UID -it ${DOCKER_REPO} /bin/bash -c "make check VECTORCONTROL=1";
     elif [ "${TRAVIS_OS_NAME}" = "osx" ]; then
       make check_posix_sitl_default;
     fi