apache2: fix a typos

fix a typos to remove a warning:
    systemd[1]: [/lib/systemd/system/apache2.service:2] Unknown lvalue
    'Decription' in section 'Unit'

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>