Add support for uppercase labels

[klaudiosinani]

Is your feature request related to a problem? Please describe.
Add the ability to switch labels to uppercase, while preserving lowercase as the default state.

Describe the solution you'd like
Include an uppercaseLabel option that can be utilized through the config() method.

Additional context

// example.js
const signale = require('signale');

signale.config({uppercaseLabel: false}); // Default state
signale.success('Successful operation');
//=>  ✔  success    Successful operation

signale.config({uppercaseLabel: true});
signale.success('Successful operation');
//=>  ✔  SUCCESS    Successful operation