patch 9.1.0928: tests: test_popupwin fails because the filter command fails

patch 9.1.0928: tests: test_popupwin fails because the filter command fails

Problem:  tests: test_popupwin fails because the filter command fails
Solution: add the "e" flag to the :s command to normalize the
          screendumps Last Change header so that it doesn't fail on
          "Pattern not found"

The test might still fail, because the "Last Change" hader should always
be part of the screendump, but at least the filter command should not
cause aborting of the test script.

Signed-off-by: Christian Brabandt <cb@256bit.org>