Update gulpfile.js to follow ES2015+ best practices

[david-poindexter]

Related to Issue

Fixes #319

Description

Update variable names in gulpfile.js to follow best practices for ES2015+.

How Has This Been Tested?

Local gulp tasks ran successfully.

Screenshots (if appropriate):

n/a

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication