TST: work around outdated travis boxes

run manual apt-get update to pick up the latest py3 security update
DOC: Fixed documentation on lstsq function on when it return an empty residuals array
Merge pull request #4457 from cimarronm/linalg_lstsq_docfix

DOC: Fixed documentation on lstsq function on when it return an empty re...
Merge pull request #4456 from juliantaylor/travis-updates

work around outdated travis boxes