Fix #2788: Add regression test

Author: nicolasstucki

tests/pos/i2788.scala

@@ -0,0 +1,9 @@
+trait Ord[A] { def less(x: A, y: A): Boolean }
+
+object Main {
+  implicit val intOrd: Ord[Int] = new Ord {  // omitted [Int] here
+    def less(x: Int, y: Int) = x < y
+  }
+
+  def main(args: Array[String]): Unit = ()
+}