TST: Silence lzma output
This was leaking to stdout when the pytest `-s` flag was used.
https://travis-ci.org/pandas-dev/pandas/jobs/614108628?utm_medium=notification&utm_source=github_status and https://travis-ci.org/pandas-dev/pandas/jobs/614108629?utm_medium=notification&utm_source=github_status are both the flaky clipboard test thanks