feat: identify direnv files as Bash

[direnv](https://direnv.net) loads files with these names into bash
subshells.

Author: nicknovitski

identify/extensions.py

@@ -319,6 +319,7 @@
     '.csslintrc': EXTENSIONS['json'] | {'csslintrc'},
     '.dockerignore': {'text', 'dockerignore'},
     '.editorconfig': {'text', 'editorconfig'},
+    '.envrc': EXTENSIONS['bash'],
     '.flake8': EXTENSIONS['ini'] | {'flake8'},
     '.gitattributes': {'text', 'gitattributes'},
     '.gitconfig': EXTENSIONS['ini'] | {'gitconfig'},
@@ -354,6 +355,7 @@
     'copy.bara.sky': EXTENSIONS['bzl'],
     'COPYING': EXTENSIONS['txt'],
     'Dockerfile': {'text', 'dockerfile'},
+    'direnvrc': EXTENSIONS['bash'],
     'Gemfile': EXTENSIONS['rb'],
     'Gemfile.lock': {'text'},
     'GNUmakefile': EXTENSIONS['mk'],