Bug#850016: dwww-convert generates Last-modified header containing invalid characters

[Hans-Georg Bork]

Hi,

had the exact same behavior with dwww 1.13.2 when trying to open any
other links from search page, e.g. News or Readme files. Adding '-' into
"Last modified" as suggested by the patch solved it for me.

Thanks to Holger for finding it and suggesting a fix.

Regards
        -- hgb