Upgrade vulnerable MarkBind dependencies

[Xenonym]

What is the purpose of this pull request? (put "X" next to an item, remove the rest)

• [X] Other, please explain: upgrading dependencies

Part of #461.

What is the rationale for this request?
npm audit (avaliable from npm >= 6.0.0) returns 434 vulnerabilities in our dependencies. We should upgrade vulnerable packages to remove these vulnerabilities.

Full results here.

What changes did you make? (Give an overview)

• I upgraded the following vulnerable packages, categoried by their function in MarkBind:
  • Live preview
    • chokidar: 1.6.1 → 2.1.5
    • live-server: 1.2.0 → 1.2.1
  • GitHub Pages deployment
    • gh-pages: 1.1.0 → 2.0.1
  • Building pages
    • fastmatter: 2.0.1 → 2.1.0
    • nunjucks: 3.0.0 → 3.2.0
    • markdown-it-table-of-contents: 0.3.2 → 0.4.3
  • Development tools
    • eslint: 4.16.0 → 5.15.3
    • jest: 22.4.3 → 24.5.0
    • lodash: 4.17.5 → 4.17.11
• I also upgraded the eslint config packages, as there are rule specifications that have changed/deprecated between the eslint versions:
  • eslint-config-airbnb-base: 12.1.0 → 13.1.0
  • eslint-plugin-import: 2.8.0 → 2.16.0
  • eslint-plugin-lodash: 2.6.1 → 5.1.0
• I updated .eslintrc.js to accommodate our current coding style and disable no-else-return and implicit-arrow-linebreak as we do not currently follow these rules.
• I changed the import order in some JS files to match the sort-import rule (package dependencies before local dependencies).

Is there anything you'd like reviewers to focus on?

• Is the current .eslintrc.js suitable now that we have updated our configs?

Testing instructions:

1. Ensure that npm audit returns 0 vulnerabilities.
2. Ensure that existing functionality under the four areas affected (live preview, GitHub Pages deployment, page building, other dev tools) function as expected.

[yamgent]

Did you test it under any big websites yet like se-book or cs2103t's website to see if anything's broken?

[yamgent]

Also npm audit now shows 1 vulnerability, which is a recent report: https://www.npmjs.com/advisories/788.

> npm audit
                                                                                
                       === npm audit security report ===                        
                                                                                


# Run `npm update js-yaml --depth 2` to resolve 1 vulnerability
                                                                                
  moderate        Denial of Service                                             
                                                                                
  Package         js-yaml                                                       
                                                                                
  Dependency of   fastmatter                                                    
                                                                                
  Path            fastmatter > js-yaml                                          
                                                                                
  More info       https://nodesecurity.io/advisories/788                        
                                                                                

[!] 1 vulnerability found - Packages audited: 483686 (476942 dev, 301 optional)
    Severity: 1 moderate

[Xenonym]

Did you test it under any big websites yet like se-book or cs2103t's website to see if anything's broken?

@yamgent yes, se-edu/se-book and nus-cs2103/website-base should still work.

Also npm audit now shows 1 vulnerability, which is a recent report: npmjs.com/advisories/788.

Thanks for the catch! fastmatter has been updated to 2.1.0 in this PR.