chore: update package.json for release typescript package

[yoshinorin]

Follow up #59

Before fix

$ npm publish --dry-run
npm WARN config global `--global`, `--local` are deprecated. Use `--location=global` instead.
npm notice 
npm notice 📦  hexo-front-matter@4.0.0
npm notice === Tarball Contents ===
npm notice 1.3kB README.md
npm notice 4.1kB lib/front_matter.ts
npm notice 1.2kB package.json
npm notice === Tarball Details ===
npm notice name:          hexo-front-matter
npm notice version:       4.0.0
npm notice filename:      hexo-front-matter-4.0.0.tgz
npm notice package size:  2.5 kB
npm notice unpacked size: 6.6 kB
npm notice shasum:        91a69c90ac02748ff0d6d149600a4fbbd2f8fb11
npm notice integrity:     sha512-034a5qZfapbb6[...]L0LFEHcK4saow==
npm notice total files:   3
npm notice
+ hexo-front-matter@4.0.0

After fix

$ npm publish --dry-run
npm WARN config global `--global`, `--local` are deprecated. Use `--location=global` instead.
npm notice 
npm notice 📦  hexo-front-matter@4.0.0
npm notice === Tarball Contents ===
npm notice 1.3kB README.md
npm notice 581B  dist/front_matter.d.ts
npm notice 4.9kB dist/front_matter.js
npm notice 5.1kB dist/front_matter.js.map
npm notice 1.3kB package.json
npm notice === Tarball Details ===
npm notice name:          hexo-front-matter
npm notice version:       4.0.0
npm notice filename:      hexo-front-matter-4.0.0.tgz
npm notice package size:  4.0 kB
npm notice unpacked size: 13.3 kB
npm notice shasum:        1aebec67db38fc16975218438a3efaf85b0c6d14
npm notice integrity:     sha512-yhDe6ScwmKLgl[...]CLRaHtbI5OTIQ==
npm notice total files:   5
npm notice
+ hexo-front-matter@4.0.0

[coveralls]

Coverage remained the same at 93.514% when pulling 75c3fc4 on yoshinorin:chore/update-package.json into 1c56d8f on hexojs:master.