config.json: update hello-world topics
config.json: update hello-world topics

Control-flow(if-else statements) was recently changed to
Control-flow(conditionals)
https://github.com/exercism/x-common/pull/484

robphoenix/exercism-go,leenipper/xgo,robphoenix/exercism-go,exercism/xgo,leenipper/xgo,exercism/xgo