Upgrade from Laravel 5.5 to 5.6

[dbudwin]

Description

Upgrade from Laravel 5.5 to 5.6. These changes are a result of following the upgrade guide. Upgrades the minimum version of PHP to 7.1.3.

Motivation and Context

Get the latest and greatest version of Laravel and dependent packages.

How Has This Been Tested?

All unit tests pass and the website works as expected.

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [X] Enhancement (non-breaking change which is not noticeable to end users)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [X] I created a feature branch and did not open a pull request from my master branch.
• [X] My code follows the code style of this project.
• [X] My change requires an update to the README and I have updated it accordingly.
• [X] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [X] This is a complete change and doesn't leave the project in a bad state.
• [X] All new and existing tests passed.