package/libuhttpd: bump to version 3.8.0

package/libuhttpd: bump to version 3.8.0

BUILD_TEST_PLUGIN has been dropped since version 3.5.0 and
https://github.com/zhaojh329/libuhttpd/commit/0b2c2f4a3bdc192fffcec6fb6fd297068b6ff873

https://github.com/zhaojh329/libuhttpd/releases/tag/v3.7.0
https://github.com/zhaojh329/libuhttpd/releases/tag/v3.8.0

Fixes:
 - http://autobuild.buildroot.org/results/0d53b561ba02db018ca90dce29e9064b12c1276b

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>