fix(meta_generator): parse correct version

[curbengh]

What does it do?

#3919 (comment)

How to test

git clone -b meta-gen https://github.com/curbengh/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[coveralls]

Coverage increased (+0.0008%) to 97.131% when pulling bb430d2 on curbengh:meta-gen into 140ed36 on hexojs:master.

[SukkaW]

@curbengh

The version is not only exposed to hexo.env.version:

hexo/lib/hexo/index.js

Line 107 in 5fba0a0

version: pkg.version,

but also exposed to hexo.version:

hexo/lib/hexo/index.js

Line 472 in 5fba0a0

Hexo.version = pkg.version;

It should be accessible in both ways.

The issue might be related to #3780.

---

Update

FYI:

hexo/test/scripts/hexo/hexo.js

Line 51 in c15ce89

hexo.version.should.eql(version);

hexo/test/scripts/hexo/hexo.js

Lines 59 to 68 in c15ce89

	hexo.env.should.eql({
	args: {},
	debug: false,
	safe: false,
	silent: false,
	env: process.env.NODE_ENV || 'development',
	version,
	cmd: '',
	init: false
	});

[SukkaW]

FYI, meta_generator filter is using hexo.version as well:

hexo/lib/plugins/filter/after_render/meta_generator.js

Line 8 in c15ce89

const hexoGeneratorTag = `<meta name="generator" content="Hexo ${this.version}">`;

[curbengh]

I'm guessing the way this/hexo is exposed is different in filter and helper.
I can confirm that meta_generator helper doesn't work currently, so this fix is necessary. I tested this fix and it works.
meta_generator filter is working.

[curbengh]

The issue might be related to #3780.

I tried revert the PR, still the same issue.