Clearing typegoose cache after destroying the module

[Goodluckhf]

This fix #41

[Goodluckhf]

@hasezoey
So will we update typegoose version here and add .deleteModel?

[hasezoey]

it will be shipped in (typegoose) 6.1.1 (not released yet)

[hasezoey]

as a note: 6.1.1 is now released

[Goodluckhf]

@hasezoey
I've updated typegoose and mongoose and add .deleteModel()

[hasezoey]

typescript version should probably be updated, reason:
in versions <3.5 the "Omit" type does not exists, and the current typescript version is "3.4.x"

(see current failing travis test)

[Goodluckhf]

@hasezoey I've tried to update typescript to latest but i got this error:

So I just increase 1 minor version

[coveralls]

Pull Request Test Coverage Report for Build 80

• 3 of 6 (50.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-4.8%) to 93.0%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/typegoose-core.module.ts	3	6	50.0%

Totals
Change from base Build 74:	-4.8%
Covered Lines:	70
Relevant Lines:	74

---

💛 - Coveralls

[hasezoey]

i think this needs to be investigated & fixed, but i think out-of-scope for this pr

[hasezoey]

@hasezoey I've tried to update typescript to latest but i got this error:

@Goodluckhf i now know where the error was (the gulp build process), fixed it, will make a new pr for updating dependencies

[kpfromer]

Looks good.