fix(config): set 'ignore' to ignores some files

[dailyrandomphoto]

Related: #25 , hexojs/hexo#3904 , hexojs/site#1195

Set default value for ignore.

ignore:
  # ignore themes/xxx/node_modules/
  - "**/node_modules/**"
  # ignore themes/xxx/.git/ and other hidden files
  - "**/.*"

This value is useful when you git clone a theme repo to /themes/ .

[SukkaW]

Hidden files and theme/**/node_modules are already ignored when processing themes, see: https://github.com/hexojs/hexo/blob/b6394c78751d2be81c3fd7c243fca37c552cd83a/lib/theme/processors/source.js#L31

[dailyrandomphoto]

Hidden files and theme/**/node_modules are already ignored when processing themes, see: https://github.com/hexojs/hexo/blob/b6394c78751d2be81c3fd7c243fca37c552cd83a/lib/theme/processors/source.js#L31

Yes, they are ignored when processing themes.

However these files are included in model('Cache'). (see this db.json.txt )

If there are many files under node_modules/, it will slow down hexo and uses a lot of memory.
This even causes this error.

Error: ENOMEM: not enough memory, open '/home/dev/test-rollback/themes/landscape/node_modules/rxjs/operator/exhaust.js'

[dailyrandomphoto]

I think it's better to handle this in lib/box/index.js instead of _config.yml on hexo@4.1 and later.

[curbengh]

I think it's better to handle this in lib/box/index.js instead of _config.yml on hexo@4.1 and later.

I agree, I plan to add **/themes/*/node_modules/** into lib/box, so that it's always ignored regardless of _config.yml (user might accidentally reset the ignore: config).

It will be part of >=4.1.1 (4.1.0 is getting long in the tooth).