Allow default import syntax from TypeScript

[unpollito]

Description

Currently, importing the library from TypeScript doesn't work as advertised. According to the types file, it should be imported like this:

import googleVerify from "google-play-billing-validator";
new googleVerify({ email: "foo", key: "bar" });

However, while this compiles, it causes a runtime error: TypeError: google_play_billing_validator_1.default is not a constructor

It's currently possible to make this work with TypeScript, but it forces the user to force a cast, which defeats the purpose of using types:

import * as googleVerify from "google-play-billing-validator";
// needs "as any", or it won't compile
new (googleVerify as any)({ email: "foo", key: "bar" });

Adding the default import syntax would allow the code from the first example to work as advertised, and is also a typical solution (e.g., off the top of my mind, Axios does this).

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Documentation:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

[vintage]

Just been integrating the lib today and hit the TypeError: google_play_billing_validator_1.default is not a constructor. Default import syntax should be definitely supported out of the box. @Deishelon got chance to take a look at it?

[Deishelon]

LGTM! Thanks 💕