package/python-pycairo: depend on python3

Since version 1.19.0 pycairo doesn't support Python 2 anymore.

Fixes:
 - http://autobuild.buildroot.net/results/4d47c71f75a61810c5f58a720245bef38b3f3db0

Signed-off-by: Asaf Kahlon <asafka7@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/python-pycairo/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_PYTHON_PYCAIRO
 	bool "python-pycairo"
+	depends on BR2_PACKAGE_PYTHON3
 	select BR2_PACKAGE_CAIRO
 	help
 	  Python interface for cairo.