message: Fix output-dir for Storybook v4.
diff: import execa from 'execa';
  import fs from 'fs';
  import path from 'path';
  +import semver from 'semver';
  import tmp from 'tmp-promise';
  import { createTask, transitionTo } from '../lib/tasks';
  @@ -20,8 +21,13 @@ const TesterSkipBuildMutation = `
  `;
  export const setSourceDir = async ctx => {
  + if (semver.lt(ctx.storybook.version, '5.0.0')) {
  + // Storybook v4 doesn't support absolute paths
  + ctx.sourceDir = 'storybook-static';
  + } else {
  const tmpDir = await tmp.dir({ unsafeCleanup: true, prefix: `chromatic-` });
  ctx.sourceDir = tmpDir.path;
  + }
  };
  export const setSpawnParams = ctx => {
  