Add parenthesis to avoid ambiguous pipe in doctest

[MeneDev]

For a doctest that uses an :inspect a warning is issued for elixir 1.8.2-otp-22

warning: parentheses are required when piping into a function call. For example:

    foo 1 |> bar 2 |> baz 3

is ambiguous and should be written as

    foo(1) |> bar(2) |> baz(3)

[antonmi]

Cool! Thank you!