Fix most instances of security vulnerabilities via upgrades.

[adunkman]

Related to #464, this PR upgrades dependencies to their latest and performs npm’s automated npm audit fix to upgrade vulnerable subdependencies when permitted.

Upgraded dependency	From	To	Release notes / Diff
fuse.js	5.0.5-beta	5.1.0	📗 / 🧮
netlify-cms	2.10.23	2.10.42	📗 / 🧮
jest	25.1.0	25.3.0	📗 / 🧮

The resulting npm audit report.

                                                                                
                       === npm audit security report ===                        
                                                                                
┌──────────────────────────────────────────────────────────────────────────────┐
│                                Manual Review                                 │
│            Some vulnerabilities require your attention to resolve            │
│                                                                              │
│         Visit https://go.npm.me/audit-guide for additional guidance          │
└──────────────────────────────────────────────────────────────────────────────┘
┌───────────────┬──────────────────────────────────────────────────────────────┐
│ Low           │ Prototype Pollution                                          │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ minimist                                                     │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Patched in    │ >=0.2.1 <1.0.0 || >=1.2.3                                    │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ http-server [dev]                                            │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ http-server > optimist > minimist                            │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://npmjs.com/advisories/1179                            │
└───────────────┴──────────────────────────────────────────────────────────────┘
found 1 low severity vulnerability in 251478 scanned packages
  1 vulnerability requires manual review. See the full report for details.

Have submitted http-party/http-server#622 for an upstream fix to the remaining vulnerability, http-server is used while running npm test. Can also move to another library, if that pull request doesn’t receive attention — will leave #464 open as a reminder.