code: function replaceVersionsObservable(name, versions) {
    return Observable.create((observer) => {
      const package = getSrcPackageFile(name);
      let pkg = readFileSync(package, 'utf8');
      const regexs = Object.keys(versions).map(key =>
        ({ expr: new RegExp(key, 'g'), key, val: versions[key] }));
      regexs.forEach(reg => {
        pkg = pkg.replace(reg.expr, reg.val);
      });
      const outPath = getDestPackageFile(name);
      writeFile(outPath, pkg, err => {
        if (err) {
          observer.error(err);
        } else {
          observer.next(pkg);
          observer.complete();
        }
      });
    });
  }
docs: Create an observable of package.json dependency version replacements.
  This keeps the dependency versions across each package in sync.
  @param {string} name
  @param {Object} versions