Update extract-text-webpack-plugin to v3, drop webpack 2 support (#225)

Author: sapegin

packages/extract-text/CHANGELOG.md

@@ -1,5 +1,9 @@
 # @webpack-blocks/extract-text - Changelog
 
+## Next release
+
+- Breaking change: drop webpack 2 support, update extract-text-webpack-plugin to v3
+
 ## 1.0.0-beta.2
 
 - Update dependency version

packages/extract-text/README.md

@@ -6,6 +6,17 @@
 
 Use this block to extract text (for example CSS) from the bundle into a separate file. Uses [Extract Text Plugin](https://github.com/webpack/extract-text-webpack-plugin).
 
+
+## Installation
+
+```sh
+# for webpack v3
+npm install --save-dev @webpack-blocks/extract-text
+# for webpack v2 install the last v1.0 beta version
+npm install --save-dev @webpack-blocks/extract-text@^1.0.0-beta.2
+```
+
+
 ## Usage
 
 ```js