Fix #1951: Email notification in text mode (#1986)
Fix #1951: Email notification in text mode (#1986)

use correct mimetype of text/plain instead of text/text

fixes #1951
naparuba/shinken,naparuba/shinken,naparuba/shinken,geektophe/shinken,naparuba/shinken,naparuba/shinken,naparuba/shinken,geektophe/shinken,geektophe/shinken,geektophe/shinken,geektophe/shinken,geektophe/shinken