update copyright year

config/_default/config.toml

@@ -1,6 +1,6 @@
 baseurl = "https://bf.mengyan1223.wang/blog/"  # End your URL with a `/` trailing slash, e.g. `https://example.com/`.
 title = "Xry111's Blog"
-copyright = "© 2017-2019 Xi Ruoyao"
+copyright = "© 2017-2020 Xi Ruoyao"
 theme = "academic"
 enableEmoji = true
 footnotereturnlinkcontents = "<sup>^</sup>"