add stub for haiku os (#93)

while haiku does have terminals, the `sys` go module currently doesn't
support haiku, and so discerning what is a terminal is prohibitively
difficult to do from go. instead we assume that it is not running from a
terminal.

isatty_others.go

diff --git a/isatty_others.go b/isatty_others.go
index b24a2fa..569113e 100644
--- a/isatty_others.go
+++ b/isatty_others.go
@@ -1,5 +1,5 @@
-//go:build (appengine || js || nacl || tinygo || wasm || wasip1 || wasip2) && !windows
-// +build appengine js nacl tinygo wasm wasip1 wasip2
+//go:build (appengine || js || nacl || tinygo || wasm || wasip1 || wasip2 || haiku) && !windows
+// +build appengine js nacl tinygo wasm wasip1 wasip2 haiku
 // +build !windows
 
 package isatty