fix abiword not working in container (#5907)

cc @rdelaage
on alpine, plugin command (used in src/node/utils/Abiword.js at line 31)
is not installed by defaut. Add this plugin when installing abiword.

Co-authored-by: ppom <>

Dockerfile

@@ -78,7 +78,7 @@ RUN  \
     apk add  \
         ca-certificates \
         git \
-        ${INSTALL_ABIWORD:+abiword} \
+        ${INSTALL_ABIWORD:+abiword abiword-plugin-command} \
         ${INSTALL_SOFFICE:+libreoffice openjdk8-jre libreoffice-common}
 
 USER etherpad