Increase IOS ASCII readFile performance

src/ios/RNFetchBlobFS.m

@@ -341,13 +341,13 @@ NSMutableDictionary *fileStreams = nil;
                     resolve([fileContent base64EncodedStringWithOptions:0]);
             }
             else if ([[encoding lowercaseString] isEqualToString:@"ascii"]) {
-                NSMutableArray * resultArray = [NSMutableArray array];
-                char * bytes = [fileContent bytes];
-                for(int i=0;i<[fileContent length];i++) {
-                    [resultArray addObject:[NSNumber numberWithChar:bytes[i]]];
-                }
+//                NSMutableArray * resultArray = [NSMutableArray array];
+//                char * bytes = [fileContent bytes];
+//                for(int i=0;i<[fileContent length];i++) {
+//                    [resultArray addObject:[NSNumber numberWithChar:bytes[i]]];
+//                }
                 if(resolve != nil)
-                    resolve(resultArray);
+                    resolve([[NSString alloc] initWithData:fileContent encoding:NSASCIIStringEncoding]);
             }
         }];
     }