Replace a sequence of <|> with choice.

Replaces `a1 <|> a2 <|> ... <|> an-1 <|> an` with `choice [ a1, a2, ..., an-1 ] <|> an` in `Idris.REPLParser` where `choice` is from package `parsers` module `Text.Parser.Combinators`.

On my machine with ghc 7.8.3 this lead to a decrease in memory usage during compilation of this module from >7GiB to ~400MiB.