Fix issue with vercel compatibility

[kaaloo]

This PR refactors dynamic requires to simpler static ones to fix the following issue in vercel deployment:

2021-02-10T17:48:10.778Z	undefined	ERROR	Cannot find module './main/packages/Cosine'
Require stack:
- /var/task/node_modules/string-comparison/lib/index.js
- /var/task/node_modules/article-parser/src/utils/chooseBestUrl.js
- /var/task/node_modules/article-parser/src/utils/parseFromHtml.js
- /var/task/node_modules/article-parser/src/main.js
- /var/task/node_modules/article-parser/index.js
- /var/task/api/index.ts
- /var/task/___vc_launcher.js
- /var/runtime/UserFunction.js
- /var/runtime/index.js
2021-02-10T17:48:10.788Z	undefined	ERROR	Did you forget to add it to "dependencies" in `package.json`?
RequestId: ea2ddc67-287f-4183-a996-6794719a4207 Error: Runtime exited with error: exit status 1
Runtime.ExitError

[Rabbitzzc]

What's wrong with changing the code before?

[kaaloo]

Hi sorry to get back to you so late. Vercel uses ncc under the hood when packaging serverless functions for deployment. Unfortunately, this means dynamic requires like the ones in the current code fail because ncc relies on static analysis of requires.