Chapter recurrent modern/lstm (#857)
Chapter recurrent modern/lstm (#857)

* fix errors in 9.2. LSTM

* fix errors in 9.2.1. Gated Memory Cell

* fix errors in 9.2.2. Implementation from Scratch

* fix errors in 9.2.3. Concise Implementation

* Update lstm.md

* Update lstm.md

* Update lstm.md

* Fixing :cite: issue

Co-authored-by: goldmermaid <fcb00cecbf879d17a80f4ce26a389eda39da7621@berkeley.edu>
d2l-ai/d2l-zh,d2l-ai/d2l-zh,mli/gluon-tutorials-zh,d2l-ai/d2l-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh