Dont use github link to line number

If any line above the linked line is ever added or removed from
chainparams.cpp, the link pointing to L.123 will continue to point to
L.123 but the start of the comment won't be there. See
andrew.yurisich.com/work/2014/07/16/dont-link-that-line-number/ for the
workaround i have used on this.