travis: redirect debug messages to stderr
travis: redirect debug messages to stderr

mattam82/coq-opam-archive,gmalecha/opam-coq-archive,ybertot/opam-coq-archive,gmalecha/opam-coq-archive,ybertot/opam-coq-archive,coq/opam-coq-archive,mattam82/coq-opam-archive,ybertot/opam-coq-archive,mattam82/coq-opam-archive,gmalecha/opam-coq-archive