travis: fix cwd when running tests

Make sure we don't go messing with the cwd when running different tests.
This way we can always assume we start in the top level source dir.

scripts/travis-build.sh

@@ -49,9 +49,10 @@ build() {
 # Do an out-of-tree build and make sure we can create a release tarball.
 build_out_of_tree() {
   mkdir -p build/native
-  cd build/native
+  pushd build/native >/dev/null
   ../../configure
   make -j${JOBS} distcheck VERBOSE=1
+  popd >/dev/null
 }
 
 main() {