update example to use feign 2.0.0 syntax

results in a 336k jar (mostly gson) which returns a github contributor list in <1s clock time.

```
$ time examples/feign-example-cli/build/github
quidryan (43)
adriancole (20)
gorzell (1)
Randgalt (1)
stonse (1)

real	0m0.930s
user	0m1.125s
sys	0m0.095s
```