Enable SVG upload without plugin

// into functions.php
<?php
function sp_enable_svg_upload( $mimes ) {
  //For security reasons only admin can uplaod svg files
  if ( !current_user_can( 'administrator' ) ) {
    return $mimes;
  }
  $mimes['svg']  = 'image/svg+xml';
  $mimes['svgz'] = 'image/svg+xml';
  return $mimes;
}
add_filter('upload_mimes', 'sp_enable_svg_upload');
?>

Or use Daryll Doyle Safe SVG plugin.