Only look for valid YAML/JSON files in the cert spec
dir (e.g. fix #33).
Update Travis to use Go 1.9 to fix a Go bug in the
user lookups (#30).
Update README to include CA file path writing.
Remove the informational message about not writing a CA file
if no file path was provided. This was useful in testing,
but has caused a great deal of confusion among users.
Bump the patch version to trigger a release using the new Go version.
Use Go-1.9 and add CA file writes to README.