Make sure we ignore hidden files in the SSL cert check

OSX creates hidden files: `./._server.key` and `./._server.crt`. The Dokku cert
plugin is choking on those files. We should probably just ignore them, and go on
with our lives

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

tests/unit/10_certs.bats

@@ -38,6 +38,13 @@ teardown() {
   assert_success
 }
 
+@test "(certs) certs:add < tar should ignore OSX hidden files" {
+  run bash -c "dokku certs:add $TEST_APP < $BATS_TEST_DIRNAME/osx_ssl_tarred.tar"
+  echo "output: "$output
+  echo "status: "$status
+  assert_success
+}
+
 @test "(certs) certs:info" {
   run bash -c "dokku certs:add $TEST_APP < $BATS_TEST_DIRNAME/server_ssl.tar && dokku certs:info $TEST_APP"
   echo "output: "$output