sealed-classes.md 错别字修改
sealed-classes.md 错别字修改

Line 10：集中->几种
hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn