update test:examples to libiconv 1.15
update test:examples to libiconv 1.15

because 1.14 wasn't running on windows rubies 2.4+ due to what appears
to be an outdated config.guess. I could have downloaded or patched with
an updated config.guess, but this seemed easier and didn't decrease test
coverage meaningfully.

flavorjones/mini_portile,luislavena/mini_portile,luislavena/mini_portile,flavorjones/mini_portile