py-pygments: updated to 2.4.2

Version 2.4.2
- Fix encoding error when guessing lexer with given ``encoding`` option

Version 2.4.1
- Updated lexers:
  * Coq
  * MSDOS Session
  * NASM
  * Objective-C
  * Prolog
  * TypeScript
- Support CSS variables in stylesheets
- Fix F# lexer name
- Fix ``TerminalFormatter`` using bold for bright text

Version 2.4.0
- Added lexers:
  * Augeas
  * BBC Basic
  * Boa
  * Charm++ CI
  * DASM16
  * FloScript
  * FreeFem++
  * Hspec
  * Pony
  * SGF
  * Slash
  * Slurm
  * Tera Term Language
  * TOML
  * Unicon
  * VBScript

- Updated lexers:
  * Apache2
  * Cypher
  * LLVM
  * Makefiles
  * PHP
  * Rust
  * SQL
  * Stan
  * Stata
  * Terraform
  * YAML

- Add solarized style
- Add support for Markdown reference-style links
- Add license information to generated HTML/CSS files
- Change ANSI color names
- Fix catastrophic backtracking in the bash lexer
- Fix documentation failing to build using Sphinx 2.0
- Fix incorrect links in the Lisp and R lexer documentation
- Fix rare unicode errors on Python 2.7
- Fix lexers popping from an empty stack
- TypoScript uses ``.typoscript`` now
- Updated Trove classifiers and ``pip`` requirements

(adam)