Incorrect highlight color in REPL for Singleton types in Union types

[newca12]

[allanrenucci]

The syntax highlighter gets confused because Int(1) | Int(2) is not valid syntax. Fixing #3683 should resolve this issue as well.

[newca12]

Ya fix the example but REPL, singleton types and union types still not made good bedfellows
scala> :type a
Int(31m10m) | Int(31m00m)