Use user defined line colors in the chart

[Beeb0p]

Description
We have a Series=>Line=Color property. However, we do not use it at all and use a hardcoded scheme instead.

Steps to reproduce the issue:

1. Add data for the chart
2. Define line color {"type":"line","series":[{"name":"Colored Chart","values":"Sheet1!$B$30:$D$30","line":{"color":"#000000"}}]

Describe the results you received:
The line in the chart has the default color.

Describe the results you expected:
The line in the chart has black color.

Output of go version:

Excelize version or commit ID:

(2.6.1)

Environment details (OS, Microsoft Excel™ version, physical, etc.):