Y-Axis of graphs start at zero

Fix the base of graph y-axes at zero to prevent misleading graphics.

My "Commits by Day" graph was looking a bit weird.
Two days appeared to show zero commits.
It turned out that the graph was "zeroed" at 130.

This change, sensibly, forces all the graphs to start at zero.
Note: "How to Lie with Statistics" was compulsory reading at University :-)