TST: clipboard warnings

[jreback]

from a master build: https://travis-ci.org/pandas-dev/pandas/jobs/418356362

the tests are failing on this build, though they do pass, not sure why its flaky.

pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame[delims]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame[utf8]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame[string]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame_sep[utf8-|]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame_sep[string-\t]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame_sep[string-,]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame_sep[long-|]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame_sep[colwidth-\t]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame_sep[mixed-\t]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_frame_sep[float-,]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_valid_encodings[delims-UTF-8]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_valid_encodings[utf8-UTF-8]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_valid_encodings[string-UTF-8]
  source:2406: DeprecationWarning: invalid escape sequence \(
pandas/tests/io/test_clipboard.py::TestClipboard::()::test_round_trip_valid_encodings[string-utf8]

[TomAugspurger]

I believe this are all fixed on master, perhaps by #22646.