Fix Java9 depreciation message

[mdedetrich]

Problem

In JD9, the base newInstance method is deprecated, i.e.

method newInstance in class Class is deprecated: see corresponding Javadoc for more information.
[error]         getClass.getClassLoader.loadClass(cfg.getString(key)).newInstance

Solution

Use the getConstructor().newInstance() instead which is not deprecated

Checklist

• Unit test all changes
• Update README.md if applicable
• Add [WIP] to the pull request title if it's work in progress
• Squash commits that aren't meaningful changes
• Run sbt scalariformFormat test:scalariformFormat to make sure that the source files are formatted

@getquill/maintainers

[mdedetrich]

Is it possible to merge this since its blocking quill from compiling on any machine with JDK9 or newer

[mdedetrich]

Many thanks.