change package name from nrpe2 to nrpe for freebsd

the package name for nrpe on freebsd is net-mgmt/nrpe, not net-mgmt/nrpe2.  per /usr/ports/MOVED, it was changed on 2013-10-04:

0 myserver(~) % grep nrpe2 /usr/ports/MOVED
net-mgmt/nrpe2|net-mgmt/nrpe|2013-10-04|Reflect the real portname

'# $FreeBSD: head/MOVED 361124 2014-07-07 19:33:00Z madpilot $
#
'# Each entry consists of a single line containing the following four
'# fields in the order named, separated with the pipe (`|') character:
#
'#     Port:     A port that was moved (category/portname)
'#     Moved to: Where the port was moved to, or which port users can
'#               and should migrate to (category/portname); no entry
'#               indicates that the port was deleted
'#     Date:     When the moving or the removal was done (YYYY-MM-DD,
'#               in PST/PDT)
'#     Why:      The reason why the port was moved or removed
#
'# Port|Moved to|Date|Why