Fix wrong external mappings in Build.scala

Author: pikinier20

project/Build.scala

@@ -325,8 +325,8 @@ object Build {
 
   lazy val scalacOptionsDocSettings = Seq(
       "-external-mappings:" +
-        ".*scala.*::scaladoc3::https://dotty.epfl.ch/api/," +
-        ".*java.*::javadoc::https://docs.oracle.com/javase/8/docs/api/",
+        ".*scala/.*::scaladoc3::https://dotty.epfl.ch/api/," +
+        ".*java/.*::javadoc::https://docs.oracle.com/javase/8/docs/api/",
       "-skip-by-regex:.+\\.internal($|\\..+)",
       "-skip-by-regex:.+\\.impl($|\\..+)",
       "-project-logo", "docs/logo.svg",