chore(deps): update minor and patch for gatsby-plugin-mdx

[wardpeet]

This PR contains the following updates:

Package	Type	Update	Change
@mdx-js/mdx (source)	devDependencies	patch	^1.6.16 -> ^1.6.18
@mdx-js/react (source)	devDependencies	patch	^1.6.16 -> ^1.6.18
debug	dependencies	minor	^4.1.1 -> ^4.2.0
js-combinatorics	devDependencies	minor	^0.5.5 -> ^0.6.1
pretty-bytes	dependencies	minor	^5.3.0 -> ^5.4.1
slugify	dependencies	patch	^1.4.4 -> ^1.4.5

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Release Notes

mdx-js/mdx

### [`v1.6.18`](https://togithub.com/mdx-js/mdx/compare/v1.6.17...v1.6.18) [Compare Source](https://togithub.com/mdx-js/mdx/compare/v1.6.17...v1.6.18) ### [`v1.6.17`](https://togithub.com/mdx-js/mdx/compare/v1.6.16...v1.6.17) [Compare Source](https://togithub.com/mdx-js/mdx/compare/v1.6.16...v1.6.17)

visionmedia/debug

### [`v4.2.0`](https://togithub.com/visionmedia/debug/releases/4.2.0) [Compare Source](https://togithub.com/visionmedia/debug/compare/4.1.1...4.2.0) ### Minor Release - Replaced phantomJS with chrome backend for browser tests - Deprecated and later removed Changelog.md in lieu of releases page - Removed bower.json ([#​602](https://togithub.com/visionmedia/debug/issues/602)) - Removed .eslintrc (since we've switched to XO) - Removed .coveralls.yml - Removed the build system that was in place for various alternate package managers - Removed the examples folder ([#​650](https://togithub.com/visionmedia/debug/issues/650)) - Switched to `console.debug` **in the browser only** when it is available ([#​600](https://togithub.com/visionmedia/debug/issues/600)) - Copied custom logger to namespace extension ([#​646](https://togithub.com/visionmedia/debug/issues/646)) - Added issue and pull request templates - Added `"engines"` key to package.json - Added ability to control `selectColor` ([#​747](https://togithub.com/visionmedia/debug/issues/747)) - Updated dependencies - Marked `supports-color` as an optional peer dependency

dankogai/js-combinatorics

### [`v0.6.1`](https://togithub.com/dankogai/js-combinatorics/compare/0.6.0...0.6.1) [Compare Source](https://togithub.com/dankogai/js-combinatorics/compare/0.6.0...0.6.1) ### [`v0.6.0`](https://togithub.com/dankogai/js-combinatorics/compare/0.5.5...0.6.0) [Compare Source](https://togithub.com/dankogai/js-combinatorics/compare/0.5.5...0.6.0)

sindresorhus/pretty-bytes

### [`v5.4.1`](https://togithub.com/sindresorhus/pretty-bytes/releases/v5.4.1) [Compare Source](https://togithub.com/sindresorhus/pretty-bytes/compare/v5.4.0...v5.4.1) - Fix `binary` and `bits` option being used together ([#​61](https://togithub.com/sindresorhus/pretty-bytes/issues/61)) [`1333349`](https://togithub.com/sindresorhus/pretty-bytes/commit/1333349) ### [`v5.4.0`](https://togithub.com/sindresorhus/pretty-bytes/releases/v5.4.0) [Compare Source](https://togithub.com/sindresorhus/pretty-bytes/compare/v5.3.0...v5.4.0) - Add [`binary`](https://togithub.com/sindresorhus/pretty-bytes#binary) option ([#​60](https://togithub.com/sindresorhus/pretty-bytes/issues/60)) [`4ef01f4`](https://togithub.com/sindresorhus/pretty-bytes/commit/4ef01f4)

simov/slugify

### [`v1.4.5`](https://togithub.com/simov/slugify/compare/v1.4.4...v1.4.5) [Compare Source](https://togithub.com/simov/slugify/compare/v1.4.4...v1.4.5)

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