fix: correct graph labels for `index.md` nodes (#431)

Ben Schlegel

2023-08-28 c35cd422c65a58f1069302aad0cf9eef7f93d987

 quartz/plugins/transformers/lastmod.ts

@@ -36,6 +36,7 @@
              } else if (source === "frontmatter" && file.data.frontmatter) {
                created ||= file.data.frontmatter.date
                modified ||= file.data.frontmatter.lastmod
                modified ||= file.data.frontmatter.updated
                modified ||= file.data.frontmatter["last-modified"]
                published ||= file.data.frontmatter.publishDate
              } else if (source === "git") {