bump libc version to fix warning in rustc v1.6
bump libc version to fix warning in rustc v1.6

libc(0.1.12) has warning to use rustc(v1.6).
```
.cargo/registry/src/github.com-88ac128001ac3a9a/libc-0.1.12/rust/src/liblibc/lib.rs:81:21:
81:39 warning: lint raw_pointer_derive has been removed: using derive
with raw pointers is ok
```

idobata/hokaido,idobata/hokaido