message: Don't mutate the versions data structure
diff: @@ -131,7 +131,7 @@ function getDependents(dependencyName) {
  function bumpVersion(bumpTarget, bumpType, bumped = new Set()) {
  const {name} = bumpTarget.info;
  - const {published, version} = versions[name];
  + const {published, version} = bumpTarget;
  if (compareVersions(published, version) > 0) {
  const message = `Local version of ${name} (${version}) is ` +
  `already ahead of published version (${published}); no need to bump.`;
  @@ -141,7 +141,6 @@ function bumpVersion(bumpTarget, bumpType, bumped = new Set()) {
  const message = `Bumping from published version of ${name} ` +
  `(${published}) to new ${bumpType} version (${bumpedVersion}).`;
  print(message);
  - versions[name].version = (versions[name].local = bumpedVersion);
  const pkg = allPackages[name];
  pkg.info.version = bumpedVersion;
  @@ -165,8 +164,8 @@ process.on('unhandledRejection', err => {
  const [bumpType, bumpTargetName] = parseArguments();
  const publishedVersions = await genPublishedVersions(packageNames);
  packageNames.forEach((name, i) => {
  - versions[name].published = publishedVersions[i];
  - versions[name].local = allPackages[name].info.version;
  + allPackages[name].published = publishedVersions[i];
  + allPackages[name].version = versions[name].version;
  });
  bumpVersion(allPackages[bumpTargetName], bumpType);
  