Use sudo when necessary for certutil (Ubuntu 16.04 at least), fixes #192

[rfay]

#192 points out that as of v1.4.0, certutil -A is not run with sufficient privileges. This seems to be a problem particularly on Ubuntu 16.04, but possibly on some other Debian-derivatives as well.

This PR checks to see if the path to the profile is writable; if it's not, it uses sudo to run certutil -A and certutil -D

[rfay]

There are testing artifacts from this PR at https://github.com/rfay/mkcert/releases/tag/v1.4.1-alpha1 - I tried it out on macOS, Ubuntu 16.04, Debian9, and Windows and it seemed to behave as expected.

[rfay]

Just want to mention that this can be vastly simplified by always sudo-ing certutil, even on all the distros where it's unnecessary. If you want that I'll be happy to re-do that way.

[topher200]

This PR resolved my issues on Ubuntu; see my comment on #192

[dangtrinhnt-mmt]

Thanks. It works. We should merge this.