Add test to demonstrate img array bug

[johnbeech]

See: #97

> [email protected] test
> node test

  ➡️ json2md
     ⚡ should support headings
     ⚡ should support blockquotes
     ⚡ should support images
     ❌ should support an array of images
     Error: Expected '![alt](source "title")\n![alt](source "title")\n![alt](source "title")\n\n![salt](sauce "heading")\n![salt](sauce "heading")\n![salt](sauce "heading")\n\n' to be '![alt](source "title")\n\n![salt](sauce "heading")\n'
         at assert (/Users/john/Local/json2md/node_modules/expect/lib/assert.js:29:9)
         at Expectation.toBe (/Users/john/Local/json2md/node_modules/expect/lib/Expectation.js:66:28)
         at Object.<anonymous> (/Users/john/Local/json2md/test/index.js:61:13)
         at Domain.<anonymous> (/Users/john/Local/json2md/node_modules/tester/lib/index.js:161:24)
         at Domain.run (node:domain:389:15)
         at module.exports (/Users/john/Local/json2md/node_modules/try-async/lib/index.js:18:5)
         at _fn (/Users/john/Local/json2md/node_modules/tester/lib/index.js:160:17)
         at process.processTicksAndRejections (node:internal/process/task_queues:81:21)

TODO: Figure out why images are duplicated when presented as an array. This PR provides test coverage.