Fix warning about DOT_FONTNAME.
Fix warning about DOT_FONTNAME.

This fix addresses the following warning printed by 1.8.9.1:

Warning: doxygen no longer ships with the FreeSans font.
You may want to clear or change DOT_FONTNAME.
Otherwise you run the risk that the wrong font is being used for dot generated graphs.

libMesh/libmesh,vikramvgarg/libmesh,pbauman/libmesh,hrittich/libmesh,dknez/libmesh,benkirk/libmesh,90jrong/libmesh,friedmud/libmesh,pbauman/libmesh,BalticPinguin/libmesh,roystgnr/libmesh,svallaghe/libmesh,pbauman/libmesh,vikramvgarg/libmesh,aeslaughter/libmesh,balborian/libmesh,aeslaughter/libmesh,pbauman/libmesh,coreymbryant/libmesh,friedmud/libmesh,svallaghe/libmesh,dschwen/libmesh,balborian/libmesh,balborian/libmesh,aeslaughter/libmesh,benkirk/libmesh,90jrong/libmesh,benkirk/libmesh,giorgiobornia/libmesh,roystgnr/libmesh,aeslaughter/libmesh,benkirk/libmesh,balborian/libmesh,balborian/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,libMesh/libmesh,friedmud/libmesh,hrittich/libmesh,dschwen/libmesh,jwpeterson/libmesh,svallaghe/libmesh,BalticPinguin/libmesh,balborian/libmesh,capitalaslash/libmesh,jwpeterson/libmesh,dknez/libmesh,dknez/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,dschwen/libmesh,hrittich/libmesh,jwpeterson/libmesh,hrittich/libmesh,capitalaslash/libmesh,hrittich/libmesh,dschwen/libmesh,vikramvgarg/libmesh,aeslaughter/libmesh,coreymbryant/libmesh,svallaghe/libmesh,BalticPinguin/libmesh,libMesh/libmesh,vikramvgarg/libmesh,pbauman/libmesh,friedmud/libmesh,vikramvgarg/libmesh,vikramvgarg/libmesh,vikramvgarg/libmesh,balborian/libmesh,libMesh/libmesh,svallaghe/libmesh,jwpeterson/libmesh,dknez/libmesh,dknez/libmesh,svallaghe/libmesh,aeslaughter/libmesh,giorgiobornia/libmesh,90jrong/libmesh,friedmud/libmesh,jwpeterson/libmesh,roystgnr/libmesh,aeslaughter/libmesh,pbauman/libmesh,90jrong/libmesh,dschwen/libmesh,hrittich/libmesh,libMesh/libmesh,dknez/libmesh,roystgnr/libmesh,benkirk/libmesh,giorgiobornia/libmesh,90jrong/libmesh,giorgiobornia/libmesh,giorgiobornia/libmesh,giorgiobornia/libmesh,dschwen/libmesh,pbauman/libmesh,roystgnr/libmesh,coreymbryant/libmesh,BalticPinguin/libmesh,benkirk/libmesh,90jrong/libmesh,vikramvgarg/libmesh,coreymbryant/libmesh,hrittich/libmesh,capitalaslash/libmesh,aeslaughter/libmesh,roystgnr/libmesh,dknez/libmesh,benkirk/libmesh,friedmud/libmesh,svallaghe/libmesh,90jrong/libmesh,90jrong/libmesh,svallaghe/libmesh,coreymbryant/libmesh,libMesh/libmesh,friedmud/libmesh,svallaghe/libmesh,giorgiobornia/libmesh,dschwen/libmesh,dknez/libmesh,libMesh/libmesh,roystgnr/libmesh,hrittich/libmesh,capitalaslash/libmesh,balborian/libmesh,balborian/libmesh,libMesh/libmesh,giorgiobornia/libmesh,hrittich/libmesh,BalticPinguin/libmesh,coreymbryant/libmesh,coreymbryant/libmesh,friedmud/libmesh,pbauman/libmesh,90jrong/libmesh,capitalaslash/libmesh,roystgnr/libmesh,aeslaughter/libmesh,benkirk/libmesh,jwpeterson/libmesh,pbauman/libmesh,capitalaslash/libmesh,friedmud/libmesh,BalticPinguin/libmesh,coreymbryant/libmesh,vikramvgarg/libmesh,balborian/libmesh,benkirk/libmesh,giorgiobornia/libmesh,dschwen/libmesh,BalticPinguin/libmesh