Taking a quick look into the sources solved my problem:
sftp: {
deploy: {
files: {
"./": "doc/**"
},
options: {
path: '<%= pkg.server.path %>',
host: '<%= pkg.server.host %>',
username: '<%= pkg.server.user %>',
password: '<%= pkg.server.password %>',
showProgress: true,
srcBasePath: 'doc/',
createDirectories: true
}
}
}