test: tests/check failed wiih error 'invalid range end'

tests/check failed on Centos 6.x because 'sed' can't
work with '[A-z]'.
It would fail with 'invalid range end' error message.

Fixed it by replace [A-z] with [A-Za-z].

Signed-off-by: Kai Zhang <kyle@zelin.io>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>