Remove __tests__ from installed files

[antonsamper]

Add files prop to package.json and include only neccesary files. Remove tests, eslint, travis etc.

[webbrain-one]

Hey! I just opened PR #43 to address this. 👋

It adds a files field to package.json so we only include the necessary files and exclude tests, eslint, travis, etc.

Take a look here: #43