Upgrade i18nspector to 0.20+ on the Jenkins slave that runs check_PO_master

ikiwiki generates things like:

#. type: Plain text
#:  
#, no-wrap

… that validate just fine with 0.20, while on wheezy-backports’ 0.17-1~bpo70+1 it triggers “E: ./wiki/src/upgrade.fr.po: syntax-error-in-po-file”. This results in quite some noise sent to -l10n@.

Parent Task: #5320 (closed)

Related issues

• Blocked by #9262 (closed)
• Blocks #10747 (closed)

Original created by @intrigeri on 10592 (Redmine)