That does not work.  I often get spurious warnings, eg in
   https://travis-ci.org/RcppCore/RcppArmadillo/builds/13615666
about not having changed the version or some minor vignette thing. Same here for Rcpp:
   https://travis-ci.org/RcppCore/Rcpp/builds/13566772

At a mininum, make this optional, say in a function 'CheckLogsForWarningAndCommitSuicide' or something. 
It is inappropriate as a default.