Fix find expression for looking up .Rcheck
Fix find expression for looking up .Rcheck

- use quoting
- limit depth
qinwf/r-travis,qinwf/r-travis,eddelbuettel/r-travis,robzhu/r-travis,robzhu/r-travis,eddelbuettel/r-travis,craigcitro/r-travis,craigcitro/r-travis