Fix flow build

Author: devongovett

scripts/build-flow.js

@@ -3,7 +3,7 @@ const fs = require('fs');
 let dir = `${__dirname}/../`;
 let index = fs.readFileSync(dir + '/node/index.d.ts', 'utf8');
 index = '// @flow\n' + index;
-index = index.replace(/export interface (.*?) \{((?:.|\n)*?)\}/g, 'export type $1 = {|$2|};');
+index = index.replace(/export interface (.*?)(?: extends (.+?))? \{((?:.|\n)*?)\}/g, (_, name, ext, contents) => `export type ${name} =${ext ? ` ${ext} &` : ''} {|${contents}|};`);
 index = index.replace(/export declare function/g, 'declare export function');
 index = index.replace("Omit<TransformOptions, 'code'>", "$Rest<TransformOptions, {|code: TransformOptions['code']|}>");