add_filter( 'the_content', function( $content ) {
  $search = '<a rel="noopener" target="_blank" href=\"http:\/\/leafletjs.com\"';
  $replace = '<a rel=\"noopener\" target=\"_blank\" href=\"http:\/\/leafletjs.com\"';
  $content = str_replace( $search, $replace, $content );

  $search = '<a rel="noopener" target="_blank" href=\"http:\/\/www.openstreetmap.org\/copyright\"';
  $replace = '<a rel=\"noopener\" target=\"_blank\" href=\"http:\/\/www.openstreetmap.org\/copyright\"';
  $content = str_replace( $search, $replace, $content );

  return $content;
}, 13 );