Datatable rowGroup with rowSpan mode: row separator line style on group break

[giovannispd]

[ ] bug report
[X ] feature request
[ ] support request => Please do not submit support request here, instead see https://forum.primefaces.org/viewforum.php?f=57

Current behavior
when group change the row separator line is the same of the other rows and distinguish is difficult

Expected behavior
is appreciated a style props (or even a line with few pixels added) to set a different line size

Please tell us about your environment:
windows 10, npm, Eclipse Oxygen.3

• React version:
  16.8.6

• PrimeReact version:
  3.1.5

• Browser:
  all

• Language: ES6/7

[mertsincan]

Added 'p-datatable-rowspan-group' class to the header of each group row.

Exp;

.p-datatable-rowspan-group {
   border-top: 2px solid red;
}