Reverted a change on default margins in line-chart.js - it was breaking some tests.
Reverted a change on default margins in line-chart.js - it was breaking some tests.

chaosmail/line-chart,pacozaa/line-chart,n3-charts/line-chart-vanilla,n3-charts/line-chart,n3-charts/line-chart-vanilla,pacozaa/line-chart,pacozaa/line-chart,chaosmail/line-chart,n3-charts/line-chart,n3-charts/line-chart,n3-charts/line-chart-vanilla,chaosmail/line-chart,pacozaa/line-chart,n3-charts/line-chart-vanilla,pacozaa/line-chart,chaosmail/line-chart,chaosmail/line-chart,n3-charts/line-chart