code: function( wcs, options, callback ) {
  	// upgrade only works for versions of svn >= 1.7
  	if ( typeof options === 'function' ) {
  		callback = options;
  		options = null;
  	}
  	if ( !Array.isArray( wcs ) ) {
  		wcs = [wcs];
  	}
  	options = options || {};
  	addExtraOptions( [ 'quiet' ], options );
  
  	checkSvnVersion( options, ">=1.7.0", function( err, isValid ) {
  		if ( err ) {
  			return callback( err );
  		}
  		if ( isValid ) {
  			executeSvn( [ 'upgrade' ].concat( wcs ), options, callback );
  		} else {
  			callback();
  		}
  	} );
  }
docs: Upgrades a given svn working copy (requires v1.7 of svn client)
  @function upgrade
  @memberof commands
  @param {Array|string} wcs - Working copy targets
  @param {object} [options] - Options object
  @param {function} [callback] - Complete callback