Fix turbo-stream MIME references

Mime-type for turbo-stream changed to `text/vnd.turbo-stream.html`

docs/handbook/02_drive.md

@@ -176,5 +176,5 @@ The reason Turbo doesn't allow regular rendering on 200 is that browsers have bu
 
 ## Streaming After a Form Submission
 
-Servers may also respond to form submissions with a [Turbo Streams](streams) message by sending the header `Content-Type: text/html; turbo-stream` followed by one or more `<turbo-stream>` elements in the response body. This lets you update multiple parts of the page without navigating.
+Servers may also respond to form submissions with a [Turbo Streams](streams) message by sending the header `Content-Type: text/vnd.turbo-stream.html` followed by one or more `<turbo-stream>` elements in the response body. This lets you update multiple parts of the page without navigating.
 <br><br>

docs/handbook/04_streams.md

@@ -56,7 +56,7 @@ You can render any number of stream elements in a single stream message from a W
 
 ## Streaming From HTTP Responses
 
-Turbo knows to automatically load stream elements when they arrive in response to form submissions with a MIME type of `text/html; turbo-stream`. Turbo itself adds this type to the `Accept` header to let the server know that these responses are possible. It's therefore easily possible to tailor your server responses to deal with both Turbo Streams and regular redirects or other responses for clients that don't want the streams (such as native applications).
+Turbo knows to automatically load stream elements when they arrive in response to form submissions with a MIME type of `text/vnd.turbo-stream.html`. Turbo itself adds this type to the `Accept` header to let the server know that these responses are possible. It's therefore easily possible to tailor your server responses to deal with both Turbo Streams and regular redirects or other responses for clients that don't want the streams (such as native applications).
 
 In a Rails controller, this would look like:
 
@@ -114,7 +114,7 @@ end
 When the form to create a new message submits to the `MessagesController#create` action, the very same partial template that was used to render the list of messages in `MessagesController#index` is used to render the turbo-stream action. This will come across as a response that looks like this:
 
 ```html
-Content-Type: text/html; turbo-stream; charset=utf-8
+Content-Type: text/vnd.turbo-stream.html; charset=utf-8
 
 <turbo-stream action="append" target="messages">
   <template>