Including *.json files to fix #725

There is a problem with the automatically exported HTML5 demos. When they use json files for dialogue by example, as in the JRPG demo, the game gets errors as it can't load those specific *.json files.
Update export_presets.cfg

Author: voylin

.github/dist/export_presets.cfg

@@ -5,7 +5,7 @@ platform="HTML5"
 runnable=true
 custom_features=""
 export_filter="all_resources"
-include_filter=""
+include_filter="*.json"
 exclude_filter=""
 export_path=""
 script_export_mode=1