chore(gitignore): update from the template-formula [skip ci]

myii · myii · commit 4636f102aebf · 2020-02-14T22:29:56.000Z
* Automated using myii/ssf-formula#132
diff --git a/.gitignore b/.gitignore
@@ -105,6 +105,7 @@ ENV/
 .mypy_cache/
 
 # Bundler
+.bundle/
 Gemfile.lock
 
 # copied `.md` files used for conversion to `.rst` using `m2r`
