gnuplot: use 'w histeps' for files_by_date.

'smooth csplines' showed negative file count sometimes, which wasn't nice ;-)

gitstats

 set ylabel "Files"
 set xtics rotate by 90
 set bmargin 6
-plot 'files_by_date.dat' using 1:2 smooth csplines
+plot 'files_by_date.dat' using 1:2 w histeps
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 		f.close()