only add end line number to url if different than start line number

[schoblaska]

I use add_current_line_on_normal_mode = false. When I want to generate a link to a specific line I use visual mode, but noticed that the URLs link to a one-line range (github.com/org/repo/file#L3-L3) instead of linking to the line (github.com/org/repo/file#L3). This change makes it so that the ending line number is only appended to the URL if it's different than the starting line number.