fix typo (hotwired#586)

README.md

@@ -146,7 +146,7 @@ Turbo can coexist with Rails UJS, but you need to take a series of upgrade steps
 
 ## Testing
 
-The [`Turbo::TestAssertions`](./lib/turbo/test_assertions.rb) concern provides Turbo Stream test helpers that assert the presence or absence ofs  s  `<turbo-stream>` elements in a rendered fragment of HTML. `Turbo::TestAssertions` are automatically included in [`ActiveSaupport::TestCase`](https://edgeapi.rubyonrails.org/classes/ActiveSupport/TestCase.html) and depend on the presence of [`rails-dom-testing`](https://github.com/rails/rails-dom-testing/) assertions.
+The [`Turbo::TestAssertions`](./lib/turbo/test_assertions.rb) concern provides Turbo Stream test helpers that assert the presence or absence ofs  s  `<turbo-stream>` elements in a rendered fragment of HTML. `Turbo::TestAssertions` are automatically included in [`ActiveSupport::TestCase`](https://edgeapi.rubyonrails.org/classes/ActiveSupport/TestCase.html) and depend on the presence of [`rails-dom-testing`](https://github.com/rails/rails-dom-testing/) assertions.
 
 The [`Turbo::TestAssertions::IntegrationTestAssertions`](./lib/turbo/test_assertions/integration_test_assertions.rb) are built on top of `Turbo::TestAssertions`, and add support for passing a `status:` keyword. They are automatically included in [`ActionDispatch::IntegrationTest`](https://edgeguides.rubyonrails.org/testing.html#integration-testing).