Fix typos in README.md

README.md

 
 ### Cancel Request
 
-After `0.7.0` it is possible to cancel a HTTP request. When the request cancel, it will definately throws an promise rejection, be sure to catch it.
+After `0.7.0` it is possible to cancel an HTTP request. When the request is cancelled, it will throw a promise rejection, be sure to catch it.
 
 ```js
 let task = RNFetchBlob.fetch('GET', 'http://example.com/file/1')