Fix FormData compatibility of Blob #44

src/android/src/main/java/com/RNFetchBlob/RNFetchBlob.java

 
     @ReactMethod
     public void slice(String src, String dest, int start, int end, String encode, Callback callback) {
-
+        RNFetchBlobFS.slice(src, dest, start, end, encode, callback);
     }
 
     @ReactMethod

src/ios/RNFetchBlobReqBuilder.m

         if([[method lowercaseString] isEqualToString:@"post"] || [[method lowercaseString] isEqualToString:@"put"]) {
             // generate octet-stream body
             if(body != nil) {
-                
+                NSString * cType = [[self class] getHeaderIgnoreCases:@"content-type" fromHeaders:mheaders];
                 // when headers does not contain a key named "content-type" (case ignored), use default content type
-                if([[self class] getHeaderIgnoreCases:@"content-type" fromHeaders:mheaders] == nil)
+                if(cType == nil)
                 {
                     [mheaders setValue:@"application/octet-stream" forKey:@"Content-Type"];
                 }

src/polyfill/File.js

   name : string = '';
 
   static build(name:string, data:any, cType):Promise<File> {
-    this.name = name
     return new Promise((resolve, reject) => {
       new File(data, cType).onCreated((f) => {
+        f.name = name
         resolve(f)
       })
     })