Y-Axis of graphs start at zero

Fix the base of graph y-axes at zero to prevent misleading graphics.

Signed-off-by: Heikki Hokkanen <hoxu@users.sf.net>

gitstats

 set output 'hour_of_day.png'
 unset key
 set xrange [0.5:24.5]
+set yrange [0:]
 set xtics 4
 set grid y
 set ylabel "Commits"
 set output 'day_of_week.png'
 unset key
 set xrange [0.5:7.5]
+set yrange [0:]
 set xtics 1
 set grid y
 set ylabel "Commits"
 set output 'month_of_year.png'
 unset key
 set xrange [0.5:12.5]
+set yrange [0:]
 set xtics 1
 set grid y
 set ylabel "Commits"
 """
 set output 'commits_by_year_month.png'
 unset key
+set yrange [0:]
 set xdata time
 set timefmt "%Y-%m"
 set format x "%Y-%m"
 """
 set output 'commits_by_year.png'
 unset key
+set yrange [0:]
 set xtics 1 rotate
 set grid y
 set ylabel "Commits"
 """
 set output 'files_by_date.png'
 unset key
+set yrange [0:]
 set xdata time
 set timefmt "%Y-%m-%d"
 set format x "%Y-%m-%d"
 """
 set output 'lines_of_code.png'
 unset key
+set yrange [0:]
 set xdata time
 set timefmt "%s"
 set format x "%Y-%m-%d"
 set terminal png transparent size 640,480
 set output 'lines_of_code_by_author.png'
 set key left top
+set yrange [0:]
 set xdata time
 set timefmt "%s"
 set format x "%Y-%m-%d"
 set terminal png transparent size 640,480
 set output 'commits_by_author.png'
 set key left top
+set yrange [0:]
 set xdata time
 set timefmt "%s"
 set format x "%Y-%m-%d"