Fix #227 lastModifed date value and format

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

                 stat.putString("path", path);
                 stat.putString("type", "asset");
                 stat.putString("size", String.valueOf(fd.getLength()));
-                stat.putString("lastModified", "0");
+                stat.putInt("lastModified", 0);
             }
             else {
                 File target = new File(path);
                 stat.putString("path", target.getPath());
                 stat.putString("type", target.isDirectory() ? "directory" : "file");
                 stat.putString("size", String.valueOf(target.length()));
-                String lastModified = String.valueOf(target.lastModified());
-                stat.putString("lastModified", lastModified);
+                int lastModified = (int) target.lastModified();
+                stat.putInt("lastModified", lastModified);
 
             }
             return stat;

src/ios/RNFetchBlobFS.m

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