Merge pull request #86 from francisco-sanchez-molina/patch-1

Lost content-length header fix

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

     public MediaType contentType() {
         return mime;
     }
-
+    
+    @Override
+    public long contentLength() {
+        return contentLength;
+    }
+    
     @Override
     public void writeTo(BufferedSink sink) throws IOException {