exit -> exist (#150)
exit -> exist (#150)

PR-URL: https://github.com/npm/npm-registry-client/pull/150
Credit: da39a3ee5e6b4b0d3255bfef95601890afd80709@antialias
Reviewed-By: da39a3ee5e6b4b0d3255bfef95601890afd80709@zkat
teddyhwang/npm-registry-client,npm/npm-registry-client