remove Boris REPL

Boris is outdated. Last commit: 9 years ago.
Use PsySH instead.

README.md

 *Libraries related to the command line.*
 
 * [Aura.Cli](https://github.com/auraphp/Aura.Cli) - Provides the equivalent of request ( Context ) and response ( Stdio ) objects for the command line interface, including Getopt support, and an independent Help object for describing commands.
-* [Boris](https://github.com/borisrepl/boris) - A tiny PHP REPL.
 * [Cilex](https://github.com/Cilex/Cilex) - A micro framework for building command line tools.
 * [CLI Menu](https://github.com/php-school/cli-menu) - A library for building CLI menus.
 * [CLIFramework](https://github.com/c9s/CLIFramework) - A command-line framework supports zsh/bash completion generation, subcommands and option constraints. It also powers phpbrew.