atom: 1.42.0 -> 1.48.0

atom-beta: 1.43.0-beta0 -> 1.49.0-beta0

This version bump includes node-gyp 3.7.0 -> 5.1.0 in Atom's
apm/package-lock.json, which, per https://github.com/nodejs/node-gyp/issues/1687
, finally allows python3 to be used instead of EOL'd python2 for
atom-package installation.