fix: fetching files renders invalid blob

README.md

@@ -121,6 +121,13 @@ fetch('/bear', {
   open(r.headers.get('location'));
   return r.json();
 })
+
+// fetch image
+fetch('https://i.imgur.com/4AiXzf8.jpg', {
+  responseType: 'blob'
+}).then( r => {
+  return r.blob();
+})
 ```
 
 * * *
@@ -140,6 +147,7 @@ Unfetch will account for the following properties in `options`:
   * `headers`: An `Object` containing additional information to be sent with the request, e.g. `{ 'Content-Type': 'application/json' }` to indicate a JSON-typed request body.
   * `credentials`: ⚠ Accepts a `"include"` string, which will allow both CORS and same origin requests to work with cookies. As pointed in the ['Caveats' section](#caveats), Unfetch won't send or receive cookies otherwise. The `"same-origin"` value is not supported. ⚠
   * `body`: The content to be transmitted in request's body. Common content types include `FormData`, `JSON`, `Blob`, `ArrayBuffer` or plain text.
+  * `responseType`: An enumerated string value specifying the [type](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/responseType) of data contained in the response, the default value of text is used.
 
 ### `response` Methods and Attributes
 These methods are used to handle the response accordingly in your Promise chain. Instead of implementing full spec-compliant [Response Class](https://fetch.spec.whatwg.org/#response-class) functionality, Unfetch provides the following methods and attributes:

src/index.mjs

@@ -2,6 +2,9 @@ export default function (url, options) {
 	options = options || {};
 	return new Promise((resolve, reject) => {
 		const request = new XMLHttpRequest();
+		if (options.responseType) {
+			request.responseType = options.responseType;
+		}
 		const keys = [];
 		const headers = {};
 
@@ -12,7 +15,7 @@ export default function (url, options) {
 			url: request.responseURL,
 			text: () => Promise.resolve(request.responseText),
 			json: () => Promise.resolve(request.responseText).then(JSON.parse),
-			blob: () => Promise.resolve(new Blob([request.response])),
+			blob: () => Promise.resolve(new Blob([request.response], {type: request.response.type})),
 			clone: response,
 			headers: {
 				keys: () => keys,