Setting.py: Change property name

[imnitishng]

Change property name in class Setting from line_number --> start_line_number

Closes #5983

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[imnitishng]

Okay so this is my second PR now Travis reports ! ! Body of HEAD commit contains too long lines. Commit body lines should not exceed 72 characters. thats fine I understand how to fix it.
The only problem is how do I change the commit message in this PR? Can I do it? Or do I have to create a new branch and then a new PR with the new commit body changes?

[imnitishng]

Can someone have a look at this PR and merge it? This is my first PR!

[frextrite]

Thanks for the PR @imnitishng. The changes look good, however, change Fixes to Closes in the PR and commit body since this is not a bug.

[imnitishng]

Done!

[frextrite]

LGTM 🎉