sbt-ghpages plugin not found ?

[rensushan]

I add this line into my plugin.sbt:

addSbtPlugin("com.typesafe.sbt" % "sbt-ghpages" % "0.6.3")

However, sbt reports:
[error] not found: https://repo1.maven.org/maven2/com/typesafe/sbt/sbt-ghpages_2.12_1.0/0.6.3/sbt-ghpages-0.6.3.pom

I checked the url and find no sbt-ghpages plugins.

I wonder how to solve this problem.

I am using sbt1.4.9 on Ubuntu 18.04.

Thanks a lot !