fixed translation of string "unknown precipitation"
# Please enter the commit message for your changes. Lines starting
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# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#	modified:   ml.po
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#	../config.guess.cdbs-orig
#	../config.sub.cdbs-orig
#	../debian/
#	../m4/libtool.m4
#	../m4/ltoptions.m4
#	../m4/ltsugar.m4
#	../m4/ltversion.m4
#	../m4/lt~obsolete.m4
#	ml.po.diff
#	ml.po~
