Fix #1401: Update outdated link to slides
Fix #1401: Update outdated link to slides

yasslab/coderdojo.jp,coderdojo-japan/coderdojo.jp,coderdojo-japan/coderdojo.jp,yasslab/coderdojo.jp,coderdojo-japan/coderdojo.jp,yasslab/coderdojo.jp,coderdojo-japan/coderdojo.jp