vpnkit is not statically linked

[thaJeztah]

As noticed in docker/docker-ce-packaging#430

Sending build context to Docker daemon  2.048kB
Step 1/3 : FROM docker.io/djs55/vpnkit@sha256:e508a17cfacc8fd39261d5b4e397df2b953690da577e2c987a47630cd0c42f8e as vpnkit
sha256:e508a17cfacc8fd39261d5b4e397df2b953690da577e2c987a47630cd0c42f8e: Pulling from djs55/vpnkit
bad55c542dc9: Pull complete 
Digest: sha256:e508a17cfacc8fd39261d5b4e397df2b953690da577e2c987a47630cd0c42f8e
Status: Downloaded newer image for djs55/vpnkit@sha256:e508a17cfacc8fd39261d5b4e397df2b953690da577e2c987a47630cd0c42f8e
 ---> e49efe6f0050
Step 2/3 : FROM alpine
 ---> e7d92cdc71fe
Step 3/3 : COPY --from=vpnkit  /vpnkit /vpnkit
 ---> 84168be1ef92
Successfully built 84168be1ef92
Successfully tagged test:latest
Dave-MBP:foo djs$ docker run -it test sh
/ # ldd /vpnkit 
	/lib/ld-musl-x86_64.so.1 (0x7fce03122000)