Add changelog entry for shell session lexer.
Add changelog entry for shell session lexer.

pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments,pathawks/pygments