chore: update online-stream.h (#1264)

Fix typos.

@@ -56,7 +56,7 @@ class OnlineStream {
    * @param frame_index  The starting frame index
    * @param n  Number of frames to get.
    * @return Return a 2-D tensor of shape (n, feature_dim).
-   *         which is flattened into a 1-D vector (flattened in in row major)
+   *         which is flattened into a 1-D vector (flattened in row major)
    */
   std::vector<float> GetFrames(int32_t frame_index, int32_t n) const;