Apply fix to #254

src/fs.js

       if(err)
         reject(new Error(err))
       else {
-        if(stat)
+        if(stat) {
+          stat.size = parseInt(stat.size)
           stat.lastModified = parseInt(stat.lastModified)
+        }
         resolve(stat)
       }
     })

src/ios/RNFetchBlobFS.m

              @"size" : size,
              @"filename" : filename,
              @"path" : path,
-             @"lastModified" : [NSNumber numberWithLong:(time_t) [lastModified timeIntervalSince1970]*1000],
+             @"lastModified" : [NSString stringWithFormat:@"%@", [NSNumber numberWithLong:(time_t) [lastModified timeIntervalSince1970]*1000]],
              @"type" : isDir ? @"directory" : @"file"
             };