feat(version): Added semver versioning flags to version command (#5670)

fixes #5670 

**Summary**

Currently, it's possible (although undocumented) to automatically bump the version by running something like `yarn version --loose-semver --new-version minor`. To me, this seems less convenient and less intuitive than something like `yarn version --minor` (closely comparable to `npm version minor`). I've added the ability to automatically increment the version with one of the flags: `--major`, `--minor`, or `--patch`. This will also satisfy feature request #5367.

**Test plan**

I've included Jest test cases for each of the new versioning flags.

__tests__/commands/version.js

@@ -133,3 +133,24 @@ test('run version and make sure commit hooks are disabled by config', async ():
     expect(spawn.mock.calls[2][0]).toEqual(gitArgs);
   });
 });
+
+test('run version with --major flag and make sure major version is incremented', (): Promise<void> => {
+  return runRun([], {gitTagVersion, major: true}, 'no-args', async (config): ?Promise<void> => {
+    const pkg = await fs.readJson(path.join(config.cwd, 'package.json'));
+    expect(pkg.version).toEqual('2.0.0');
+  });
+});
+
+test('run version with --minor flag and make sure minor version is incremented', (): Promise<void> => {
+  return runRun([], {gitTagVersion, minor: true}, 'no-args', async (config): ?Promise<void> => {
+    const pkg = await fs.readJson(path.join(config.cwd, 'package.json'));
+    expect(pkg.version).toEqual('1.1.0');
+  });
+});
+
+test('run version with --patch flag and make sure patch version is incremented', (): Promise<void> => {
+  return runRun([], {gitTagVersion, patch: true}, 'no-args', async (config): ?Promise<void> => {
+    const pkg = await fs.readJson(path.join(config.cwd, 'package.json'));
+    expect(pkg.version).toEqual('1.0.1');
+  });
+});

src/cli/commands/version.js

@@ -21,6 +21,9 @@ function isValidNewVersion(oldVersion: string, newVersion: string, looseSemver:
 export function setFlags(commander: Object) {
   commander.description('Update the version of your package via the command line.');
   commander.option(NEW_VERSION_FLAG, 'new version');
+  commander.option('--major', 'auto-increment major version number');
+  commander.option('--minor', 'auto-increment minor version number');
+  commander.option('--patch', 'auto-increment patch version number');
   commander.option('--message [message]', 'message');
   commander.option('--no-git-tag-version', 'no git tag version');
   commander.option('--no-commit-hooks', 'bypass git hooks when committing new version');
@@ -77,6 +80,17 @@ export async function setVersion(
     throw new MessageError(reporter.lang('invalidVersion'));
   }
 
+  // get new version by bumping old version, if requested
+  if (!newVersion) {
+    if (flags.major) {
+      newVersion = semver.inc(oldVersion, 'major');
+    } else if (flags.minor) {
+      newVersion = semver.inc(oldVersion, 'minor');
+    } else if (flags.patch) {
+      newVersion = semver.inc(oldVersion, 'patch');
+    }
+  }
+
   // wasn't passed a version arg so ask interactively
   while (!newVersion) {
     // make sure we're not running in non-interactive mode before asking for new version