COPY incorrectly flags JSON's closing bracket as an invalid argument

[rcjsuen]

Docker will happily build the following Dockerfile but the validator incorrectly flags the closing bracket as an error. Caused by implementing #14.

FROM alpine
COPY [ "t1.txt", "t2.txt", "./" ]

$ docker build .
Sending build context to Docker daemon  1.696MB
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 : COPY [ "t1.txt", "t2.txt", "./" ]
 ---> 5c017e611051
Successfully built 5c017e611051

$ dockerfile-utils lint .\Dockerfile.1
Line: 2
COPY [ "t1.txt", "t2.txt", "./" ]
                                ^
Error: When using COPY with more than one source file, the destination must be a directory and end with a / or a \