correct typings for mongoose model

[sojharo]

Types should not extend Document as per discussion in #88

[lorensr]

Hey @sojharo, sorry for the delay, and thanks for the contribution! Did you test the types manually for both MongoDB Collections and Mongoose Models? If you feel like an automated test (just running tsc on an example ts file), that would be helpful ☺️

[sojharo]

Hey, I had the library installed in my current project and went into node_modules folder to do the changes and then test with my current project. I was able to reproduce the issue and then solve it with these changes in index.d.ts which are in this PR. When I run the project, I compile it using sucrase-node library so it compiles the typescript to javascript.

[andrmaz]

@lorensr Any progress on this PR ?

[sojharo]

Hey, yes. I had tested them with tsc and also tested it with my project by doing these changes directly inside installed version inside node_modules folder.