Won't build on Alpine

Got this after downloading the rust toolchain to the image :( apparently Alpine isn't supported?
```
  Downloaded arg_enum_proc_macro v0.3.4
error: cannot produce cdylib for `pdq v0.1.0
(/usr/local/bundle/bundler/gems/pdq-ruby-9176b44deb96/ext/pdq)` as the target
`x86_64-unknown-linux-musl` does not support these crate types
make: *** [Makefile:571: target/release/libpdq.so] Error 101
```

