Bump css-loader from 5.2.0 to 5.2.6

[nelsonni]

Description:

With the upgrade to node-loader v2.0.0 (see #430), the minimum required version of Node.js is 10.13. However, additional updates have increased the version within Synectic to be >12 and therefore caused the following error to appear on compile:

DeprecationWarning: Use of deprecated folder mapping "./" in the "exports" field module resolution of the package at /Users/nelsonni/Workspace/synectic/node_modules/postcss/package.json

This PR resolves #454, and signifies the following version changes:

• MAJOR version increase
• MINOR version increase
• PATCH version increase

Changes:

This PR makes the following changes:

• Bump css-loader from 5.2.0 to 5.2.6 to also increase postcss version to >8.1.5 to gain a fix for PostCSS in Node.js 12+ throws DeprecationWarning #454.

Checklist:

Before submitting this PR, I have verified that my code:

• Resides on a fix/ or feature/ branch that was initially branched off from development.
• Passes code linting (yarn lint) and unit testing (yarn test).
• Successfully builds a distribution package (yarn package).

Additionally, I have verified that:

• My name is listed in the Contributors section, or this PR includes a request to add my name.
• I have read and am aware of the CONTRIBUTING guide for this project.