Update default Content-Type to reflect the one used by cable_ready

Since stimulusreflex/cable_ready#260, `cable_ready` changed its Content-Type to `text/vnd.cable-ready.json`.
This commit updates the default one used to be compatible with `cable_ready`.

docs/src/_documentation/how_tos/05-integrate-cablecar.md

@@ -38,12 +38,12 @@ mrujs.start({
 Now, any link or form with `data-method="<method>"` or `data-remote="true"` will have the following `Accept` header:
 
 ```js
-"application/vnd.cable-ready.json, */*"
+"text/vnd.cable-ready.json, */*"
 ```
 
 which means any link or form with `data-method="<method>"` or `data-remote="true"` will
 perform an AJAX request, return JSON if it finds a CableCar response from your Rails
-server (or any Ruby server which provides a `Content-Type: application/vnd.cable-ready.json`
+server (or any Ruby server which provides a `Content-Type: text/vnd.cable-ready.json`
 header), and then automatically perform CableCar operations defined in the JSON payload
 return.
 

plugins/src/cableCar.ts

@@ -13,7 +13,7 @@ export class CableCar {
 
   constructor (cableReady: CableReady, { mimeType }: CableCarConfig = {}) {
     this.cableReady = cableReady
-    this.mimeType = (mimeType ?? 'application/vnd.cable-ready.json')
+    this.mimeType = mimeType ?? "text/vnd.cable-ready.json";
     this.boundPerform = this.perform.bind(this) as EventListener
   }
 

test/js/plugins/cableCar.ts

@@ -15,7 +15,7 @@ describe('CableCar with standard config', () => {
   })
 
   it('Should return true for the given content type', () => {
-    assert(cableCar.isCableReadyResponse("application/vnd.cable-ready.json; charset='utf-8'"))
+    assert(cableCar.isCableReadyResponse("text/vnd.cable-ready.json; charset='utf-8'"))
   })
 
   it('Should return true for the given content type', () => {