Update mocha version to remove security audit warnings from npm

[multics]

** READ THIS FIRST! **

When doing npm install, it complains potential security vulnerabilities from mocha package as followings:

added 30 packages from 300 contributors and audited 30 packages in 5.595s
found 3 vulnerabilities (1 low, 1 high, 1 critical)
  run `npm audit fix` to fix them, or `npm audit` for details
oauth2orize(master) $ npm audit
                                                                               
                       === npm audit security report ===                        
                                                                                
# Run  npm install --save-dev mocha@5.2.0  to resolve 3 vulnerabilities
SEMVER WARNING: Recommended action is a potentially breaking change
┌───────────────┬──────────────────────────────────────────────────────────────┐
│ Low           │ Regular Expression Denial of Service                         │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ debug                                                        │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ mocha [dev]                                                  │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ mocha > debug                                                │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://nodesecurity.io/advisories/534                       │
└───────────────┴──────────────────────────────────────────────────────────────┘


┌───────────────┬──────────────────────────────────────────────────────────────┐
│ High          │ Regular Expression Denial of Service                         │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ minimatch                                                    │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ mocha [dev]                                                  │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ mocha > glob > minimatch                                     │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://nodesecurity.io/advisories/118                       │
└───────────────┴──────────────────────────────────────────────────────────────┘


┌───────────────┬──────────────────────────────────────────────────────────────┐
│ Critical      │ Command Injection                                            │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ growl                                                        │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ mocha [dev]                                                  │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ mocha > growl                                                │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://nodesecurity.io/advisories/146                       │
└───────────────┴──────────────────────────────────────────────────────────────┘


found 3 vulnerabilities (1 low, 1 high, 1 critical) in 30 scanned packages
  3 vulnerabilities require semver-major dependency updates.

Use npm audit fix --force, and mocha was update to version 5.2.0, and the vulnerability complains go away.

Checklist

• I have read the CONTRIBUTING guidelines.
• I have added test cases which verify the correct operation of this feature or patch.
• I have added documentation pertaining to this feature or patch.
• The automated test suite ($ make test) executes successfully.
• The automated code linting ($ make lint) executes successfully.

[coveralls]

Coverage remained the same at 99.789% when pulling 3d632f1 on multics:master into 70608ed on jaredhanson:master.