Prefer const over let

[LinusU]

In order to comply with this new standard rule ☺️

standard/eslint-config-standard#133

Description

Changed from let to const where the binding never changed

Motivation and Context

It complies with the next version of Standard

How Has This Been Tested?

Ran a local version of standard

Screenshots (if appropriate):

Types of changes

• Bugfix
• Feature
• Performance Improvement
• Tests (fix, improvement, new tests)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Breaking change (fix or feature that would cause existing functionality to change)
• Other... Please describe:

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have run npm test locally and all tests are passing.
• I have added/updated tests for any new behavior.
• I have reviewed the guidelines for contributing to this repository.

[LinusU]

@ahmadnassri would you mind restarting the build for Node.js 8, seems like a temporary error during the install phase (npm ci)

[ahmadnassri]

resolved in v3.0.1