Update requirements-predeploy.txt

Former-commit-id: f8a87aa

Author: Xing Han Lu

apps/dash-peaky-finders/requirements-predeploy.txt

@@ -58,7 +58,7 @@ jupyterlab-widgets==1.0.0
 kiwisolver==1.3.1
 kombu==5.0.2
 korean-lunar-calendar==0.2.1
-lxml
+lxml==3.*
 MarkupSafe==1.1.1
 matplotlib==3.3.4
 mistune==0.8.4