Update README.md

Author: danieluhl

Diff for: README.md

@@ -52,7 +52,7 @@ It also watches your files and restarts the dev server on change. Note: if you a
 - Function signatures follow the [AWS event handler](https://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-handler.html) syntax but must be named `handler`. [We use Node v8](https://www.netlify.com/blog/2018/04/03/node.js-8.10-now-available-in-netlify-functions/) so `async` functions **are** supported ([beware common mistakes](https://serverless.com/blog/common-node8-mistakes-in-lambda/)!). Read [Netlify Functions docs](https://www.netlify.com/docs/functions/#javascript-lambda-functions) for more info.
 
 <details>
-<summary><b>Environment variables in build and branch contextx</b>
+<summary><b>Environment variables in build and branch context</b>
 
 Read Netlify's [documentation on environment variables](https://www.netlify.com/docs/continuous-deployment/#build-environment-variables).
 `netlify-lambda` should respect the env variables you supply in `netlify.toml` accordingly (except for deploy previews, which make no sense to locally emulate).