travis.yml: add libboost-dev dep
travis.yml: add libboost-dev dep

ajjl/mlpack,ajjl/mlpack,ajjl/mlpack,stereomatchingkiss/mlpack,minhpqn/mlpack,darcyliu/mlpack,trungda/mlpack,palashahuja/mlpack,ersanliqiao/mlpack,erubboli/mlpack,ranjan1990/mlpack,ersanliqiao/mlpack,thirdwing/mlpack,Azizou/mlpack,datachand/mlpack,theranger/mlpack,minhpqn/mlpack,stereomatchingkiss/mlpack,bmswgnp/mlpack,thirdwing/mlpack,datachand/mlpack,Azizou/mlpack,lezorich/mlpack,chenmoshushi/mlpack,ersanliqiao/mlpack,stereomatchingkiss/mlpack,datachand/mlpack,chenmoshushi/mlpack,bmswgnp/mlpack,BookChan/mlpack,thirdwing/mlpack,minhpqn/mlpack,theranger/mlpack,ranjan1990/mlpack,lezorich/mlpack,darcyliu/mlpack,palashahuja/mlpack,Azizou/mlpack,theranger/mlpack,erubboli/mlpack,trungda/mlpack,bmswgnp/mlpack,lezorich/mlpack,BookChan/mlpack,palashahuja/mlpack,ranjan1990/mlpack,erubboli/mlpack,trungda/mlpack,BookChan/mlpack,chenmoshushi/mlpack,darcyliu/mlpack