Do not include source code in the npm package

**What version of Ajv are you using? Does the issue happen if you use the latest version?**
Ajv version: *7.0.3*. Typescript version should not matter I guess, but anyway I am using the version *4.1.3*

**What results did you expect?**
I was not expecting to get the typescript source code in the npm package.

**Are you going to resolve the issue?**
I can help if you point me where exactly the build and publish of this library is managed.