Fix format string in printf

I knew this was hanging out there, but Antagoynm found it before I was
able to resolve it.  There was a message from shellcheck regarding this
one:
	SC2059: Don't use variables in the printf format string. Use
printf "..%s.." "$foo".

Should resolve #181

Signed-off-by: Eric F Crist <ecrist@secure-computing.net>

easyrsa3/easyrsa

@@ -479,7 +479,7 @@ current CA keypair. If you intended to start a new CA, run init-pki first."
 	echo
 	if [ "$kpass" = "$kpass2" ];
 	then
-		printf "$kpass" > "$out_key_pass_tmp"
+		printf "%s" "$kpass" > "$out_key_pass_tmp"
 	else
 		die "Passphrases do not match."
 	fi