Fix placeholder width for nuxeo-user-suggestion with multiple=true

It has been observed that the placeholder is partially displayed in a "nuxeo-user-suggestion" element with multiple=true.

Pre-requisite: copy the attached jar to nxserver/plugins/

Steps to reproduce:

1. log in as Administrator
2. go to the personal workspace and create a File document
3. start the workflow "notif"
4. click on the button "Process" to display the task
5. click on the button Add for the "Stage" field
6. a popup is displayed where a dropdown menu can be used to select the values for "List User Stage"
7. observe that the text of the placeholder is partially displayed (you should see only Please whereas the entire text is "Please enter Username or UserID"

Expected behavior: the text of the placeholder is fully displayed