Fixing compilation error for 2.12 and below.

Author: martingd

shared/src/test/scala/scala/util/parsing/combinator/lexical/StdLexicalTest.scala

@@ -13,7 +13,7 @@ class StdLexicalTest {
     var scanner: Reader[lexer.Token] = new lexer.Scanner(input)
     val listBuffer = ListBuffer[lexer.Token]()
     while (!scanner.atEnd) {
-      listBuffer.addOne(scanner.first)
+      listBuffer += scanner.first
       scanner = scanner.rest
     }
     listBuffer.toList
@@ -33,7 +33,7 @@ class StdLexicalTest {
   @Test
   def parseDelimiters: Unit = {
     object Lexer extends StdLexical
-    Lexer.delimiters addAll List("(", ")", "=>")
+    Lexer.delimiters ++= List("(", ")", "=>")
     import Lexer._
     assertEquals(
       List(Keyword("("), Identifier("id1"), Keyword(")"), Keyword("=>"), Identifier("id2")),