plugins/redirects: Fix tabs are parsed as part of the source

[SmithChart]

Until now the columns of a .rr-files could only be separated by spaces. This regularly leads to not working redirects, where the generated source-file would contain tabs as part of the file name.

This comes down to how the regex parses the file: Before this change only spaces were not part of source and destination - but other whitespace was ok.

With this change source and destination can not contain any whitespace. Thus tabs are parsed as separators - as one would expect.