fix: add support for single quote in JSONInstruction

[tdurieux]

Add support for this type of instructions SHELL ['ls', '-l']

[rcjsuen]

Note

The exec form is parsed as a JSON array, which means that you must use double-quotes (") around words not single-quotes (').

According to the documentation, CMD and ENTRYPOINT enforces this as a requirement so I will need to put some thought into the right approach here.