t/test-meta.sh: replace 'diff -u5' with 'diff -U5'.
t/test-meta.sh: replace 'diff -u5' with 'diff -U5'.

The old-style option is obsolete.

Signed-off-by: Avery Pennarun <e03ccfb89d416c4697ad6970ce86a92c1c28a78e@gmail.com>

mhoeher/bup,tjanez/bup,gevaerts/bup,mhoeher/bup,mhoeher/bup,ToxicFrog/bup,apenwarr/bup,jbaber/bup,tjanez/bup,ToxicFrog/bup,pombredanne/bup,ToxicFrog/bup,pombredanne/bup,mhoeher/bup,gevaerts/bup,pombredanne/bup,pombredanne/bup,gevaerts/bup,gevaerts/bup,apenwarr/bup,apenwarr/bup,jbaber/bup,gevaerts/bup,tjanez/bup,ToxicFrog/bup,jbaber/bup,pombredanne/bup,jbaber/bup,tjanez/bup,jbaber/bup,ToxicFrog/bup,pombredanne/bup,mhoeher/bup,mhoeher/bup,jbaber/bup,tjanez/bup,tjanez/bup,apenwarr/bup