D3.js axis gridlines width < 1.0
minor Gridelines
d3 minor lines 3
d3 minor lines 4
d3 minor lines 5
d3 minor lines 6
d3.js major minor tick style 1
d3.js major minor tick style 2
d3.js major minor tick style 3
D3.js axis gridlines width > 1.0
D3 time.scale minor lines