scripts: json2code: explicitly use python3 as interpreter
scripts: json2code: explicitly use python3 as interpreter

Python 3 is now the default in most Linux environments.

Signed-off-by: Julien Olivain <7fdfe229fce69a4d7f38653f3755ccbae5703f88@cotds.org>

jolivain/glslsandbox-player,jolivain/glslsandbox-player,jolivain/glslsandbox-player,jolivain/glslsandbox-player