getCosignatories should return `Promise<PublicAccount[]>` instead of `Promise<object[]>`

[Jonathan Tey]

getCosignatories should return Promise<PublicAccount[]> instead of Promise<object[]>. See https://github.com/nemtech/nem2-sdk-typescript-javascript/blob/master/src/model/account/MultisigAccountInfo.ts line 46

public getCosignatories(urls: string): Promise<object[]> {
...

Source: https://github.com/luxtagofficial/Apostille-library/blob/master/src/ApostilleAccount.ts

[Al-Khawarizmi]

@aizaiz can you please look into this?