Tree: Fix the pipe symbol to match the other UTF-8 symbols used

The "branching" symbols used to print the tree are UTF-8 characters.
Make the pipe symbol be the matching UTF-8 character to close the tiny gap
between symbols visible in the tree before.

core/shared/src/main/scala/coursier/util/Tree.scala

@@ -36,7 +36,7 @@ object Tree {
     def showLine(isLast: Seq[Boolean]): String = {
       val initPrefix = init(isLast) {
         case true => "   "
-        case false => "|  "
+        case false => "│  "
       }.mkString
 
       val lastPrefix = last(isLast) {