[etherpad-web/oscp-backend] Try to install etherpad deps separately

[Bartłomiej Piotrowski <bpiotrowski src gnome org>]

commit f0f1edab97bbf3d7623bc83d8559bd1a2dca6703
Author: Bartłomiej Piotrowski <bpiotrowski gnome org>
Date:   Wed May 13 10:22:33 2020 +0200

    Try to install etherpad deps separately

 Dockerfile | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/Dockerfile b/Dockerfile
index fb692d1..02cf6f1 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -19,6 +19,7 @@ WORKDIR /opt/etherpad
 
 # Install a few default plugins:
 SHELL ["/usr/bin/scl", "enable", "rh-nodejs10"]
+RUN npm install
 RUN npm install ep_adminpads \
     ep_align \
     ep_headings2 \