.gitignore: Also ignore _build
.gitignore: Also ignore _build

This is automake's default build directory.

resin-io/ostree,gatispaeglis/ostree,leandrosansilva/ostree,gatispaeglis/ostree,GNOME/ostree,GNOME/ostree,leandrosansilva/ostree,gatispaeglis/ostree,sujitfulse/ostree,resin-io/ostree,GNOME/ostree,sujitfulse/ostree,gatispaeglis/ostree,leandrosansilva/ostree,sujitfulse/ostree,leandrosansilva/ostree,GNOME/ostree,GNOME/ostree,sujitfulse/ostree,leandrosansilva/ostree,resin-io/ostree,sujitfulse/ostree,gatispaeglis/ostree,gatispaeglis/ostree,resin-io/ostree,resin-io/ostree