docs: remove warning about master branch and v4 status

README.md

@@ -1,7 +1,5 @@
 # Cal-HeatMap [![Coverage Status](https://coveralls.io/repos/wa0x6e/cal-heatmap/badge.svg?branch=master&service=github)](https://coveralls.io/github/wa0x6e/cal-heatmap?branch=master) [![npm version](https://badge.fury.io/js/cal-heatmap.svg)](https://badge.fury.io/js/cal-heatmap) [![node](https://github.com/wa0x6e/cal-heatmap/actions/workflows/test.yml/badge.svg?branch=master)](https://github.com/wa0x6e/cal-heatmap/actions/workflows/test.yml) [![node](https://github.com/wa0x6e/cal-heatmap/actions/workflows/lint.yml/badge.svg?branch=master)](https://github.com/wa0x6e/cal-heatmap/actions/workflows/lint.yml)
 
-### Current `master` branch is for next version 4, and not stable enough for production
-
 > Cal-Heatmap is a javascript module to create calendar heatmap to visualize time series data, a la github contribution graph
 
 This module will help you to create a calendar, like the _[contribution calendar](https://github.com/blog/1360-introducing-contributions)_ appearing on each github user's page, but with navigation and more controls on the data formatting.