GOCBC-304: Corrected certificate authenticator name.

Motivation
----------
In order to maintain consistency between all SDKs, the name
of our certificate-based authenticator is intended to be
CertAuthenticator as opposed to the current name.

Changes
-------
Renamed CertificateAuthenticator to CertAuthenticator and added
a deprecated backwards-compatible alias from the old name to
the new name.

Change-Id: Ie8657b5e65a67248618b63c3a9068207ca56bfa7
Reviewed-on: http://review.couchbase.org/94436
Reviewed-by: Charles Dixon <chvckd@gmail.com>
Tested-by: Brett Lawson <brett19@gmail.com>

auth.go

@@ -126,14 +126,18 @@ func (ra PasswordAuthenticator) Credentials(req AuthCredsRequest) ([]UserPassPai
 	}}, nil
 }
 
-// CertificateAuthenticator implements an Authenticator which can be used with certificate authentication.
-type CertificateAuthenticator struct {
+// CertAuthenticator implements an Authenticator which can be used with certificate authentication.
+type CertAuthenticator struct {
 }
 
 // Credentials returns the credentials for a particular service.
-func (ca CertificateAuthenticator) Credentials(req AuthCredsRequest) ([]UserPassPair, error) {
+func (ca CertAuthenticator) Credentials(req AuthCredsRequest) ([]UserPassPair, error) {
 	return []UserPassPair{{
 		Username: "",
 		Password: "",
 	}}, nil
 }
+
+// CertificateAuthenticator is included for backwards compatibility only.
+// Deprecated: Use CertAuthenticator instead.
+type CertificateAuthenticator CertAuthenticator