Don't overwrite appsscript.json on create

[sqrrrl]

Noticed that create does a fetch of the newly created project and overwrites any local files. In some cases that's undesirable (e.g. clone a project from git, create a new project before pushing code.) Would be helpful to skip the fetch if current directory looks like a valid project (e.g. appsscript.json present)

[grant]

Will close after published to npm.