Validator should detect invalid duration that includes a hyphen

[rcjsuen]

FROM alpine
HEALTHCHECK --interval=5s-10ms CMD ls

$ docker build .
Sending build context to Docker daemon  1.693MB
Step 1/2 : FROM alpine
latest: Pulling from library/alpine
ff3a5c916c92: Pull complete
Digest: sha256:7df6db5aa61ae9480f52f0b3a06a140ab98d427f86d8d5de0bedab9b8df6b1c0
Status: Downloaded newer image for alpine:latest
 ---> 3fd9065eaf02
Step 2/2 : HEALTHCHECK --interval=5s-10ms CMD ls
time: unknown unit s- in duration 5s-10ms

A duration of 5s-10ms should be flagged as an error by the validator.

> dockerfile-utils lint Dockerfile
>