refactor: add 'md' to FILE_TYPES

[lmlife2016]

when I use Chai Plugin for Snapshot Testing with Karma, run script 'karma start', there will show some warning like this in terminal: '[middleware:karma]: Invalid file type (md), defaulting to js.'
this change could clear the warning

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✅ Build karma 235 completed (commit 321ea76880 by @lmlife2016)

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✅ Build karma 2633 completed (commit 321ea76880 by @lmlife2016)

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✅ Build karma 234 completed (commit 321ea76880 by @lmlife2016)

[lmlife2016]

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[devoto13]

Thanks for the PR @lmlife2016, but this fix does not seem to be necessary.

You can override type parameter in your Karma config file if you want your .md files to be treated as JS files and included as script tags.

E.g.

    files: [
      { pattern: "**/__snapshots__/**/*.md", type: "js" },
      "__tests__/index.js"
    ],

Let me know if this solves your problem?

[lmlife2016]

Thanks for the PR @lmlife2016, but this fix does not seem to be necessary.

You can override type parameter in your Karma config file if you want your .md files to be treated as JS files and included as script tags.

E.g.

    files: [
      { pattern: "**/__snapshots__/**/*.md", type: "js" },
      "__tests__/index.js"
    ],

Let me know if this solves your problem?

It's good! Thank you every much!