ci/run_cpplint.py: trivial bugfix
ci/run_cpplint.py: trivial bugfix

cpplint.py outputs its result to stderr.
To save the results to a file, stderr needs to be
captured (stdout is blank in this case).

cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs