Fix use of execute() to get swapname

[shanesmith]

The output of execute('swapname') includes a leading newline character which makes the swapinfo() call later on fail. Fixed by trimming the output.

:echo execute('swapname')

/path/to/afile.swp

:echo swapinfo(execute('swapname'))
{'error': 'Cannot open file'}

:echo swapinfo(trim(execute('swapname')))
{'pid': 1234, [...]}

[chrisbra]

thanks!