package/python-ujson: needs python3

python 2 support has been dropped since version 3.0.0 and
https://github.com/ultrajson/ultrajson/commit/0673d237cf5589a2a059771f694d5fbc5a293b13
resulting in the following build failure since bump to version 4.1.0 in
commit a47f332a20bf3f79ef4903c8ddd2b7917217e354:

./python/ujson.c:79:15: error: variable 'moduledef' has initializer but incomplete type
   79 | static struct PyModuleDef moduledef = {
      |               ^~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/61cc675281ba25d6ebee4892175e9c7222aabb79

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/python-ujson/Config.in

@@ -1,7 +1,8 @@
 config BR2_PACKAGE_PYTHON_UJSON
 	bool "python-ujson"
+	depends on BR2_PACKAGE_PYTHON3
 	help
 	  UltraJSON is an ultra fast JSON encoder and decoder written
-	  in pure C with bindings for Python 2.5+ and 3.
+	  in pure C with bindings for Python 3.
 
 	  https://pypi.python.org/pypi/ujson