Update libiconv to 1.15
Update libiconv to 1.15

It's 1.15 in Chef 12. I think when omnibus overrides were changed around
this slipped through the cracks.

Signed-off-by: Tim Smith <764ef62106582a09ed09dfa0b6bff7c05fd7d1e4@chef.io>

gene1wood/chef,MsysTechnologiesllc/chef,tas50/chef-1,jonlives/chef,higanworks/chef,sanditiffin/chef,tomdoherty/chef,nathwill/chef,mal/chef,tas50/chef-1,tomdoherty/chef,nvwls/chef,Tensibai/chef,jaymzh/chef,Ppjet6/chef,nathwill/chef,chef/chef,mal/chef,martinisoft/chef,gene1wood/chef,Ppjet6/chef,MsysTechnologiesllc/chef,tomdoherty/chef,jaymzh/chef,mal/chef,Tensibai/chef,juliandunn/chef,chef/chef,mwrock/chef,martinisoft/chef,nvwls/chef,Tensibai/chef,mwrock/chef,tomdoherty/chef,juliandunn/chef,jaymzh/chef,sanditiffin/chef,mal/chef,jonlives/chef,nvwls/chef,higanworks/chef,mwrock/chef,tas50/chef-1,jaymzh/chef,nvwls/chef,nathwill/chef,mattray/chef,martinisoft/chef,Ppjet6/chef,nvwls/chef,mwrock/chef,sanditiffin/chef,jonlives/chef,sanditiffin/chef,gene1wood/chef,martinisoft/chef,higanworks/chef,jonlives/chef,mal/chef,juliandunn/chef,nathwill/chef,mal/chef,Ppjet6/chef,gene1wood/chef,sanditiffin/chef,martinisoft/chef,mattray/chef,chef/chef,nathwill/chef,nathwill/chef,sanditiffin/chef,jonlives/chef,higanworks/chef,tomdoherty/chef,chef/chef,MsysTechnologiesllc/chef,mattray/chef,higanworks/chef,mattray/chef,Ppjet6/chef,Tensibai/chef,juliandunn/chef,Ppjet6/chef,Tensibai/chef,tas50/chef-1,nvwls/chef,jonlives/chef,juliandunn/chef,mattray/chef,MsysTechnologiesllc/chef