Bump WP Coding Standards Dependency from ^2.3 → ^3.0

[ggwicz]

The 2.x versions of the WP Coding Standards are often producing the following errors when you run phpcs, which pollutes the output:

FILE: stellarwp-web-common/Plugin.php
------------------------------------------------------------------------------------------------
FOUND 2 ERRORS AFFECTING 1 LINE
------------------------------------------------------------------------------------------------
 1 | ERROR | Missing file doc comment (Squiz.Commenting.FileComment.Missing)
 1 | ERROR | An error occurred during processing; checking has been aborted. The error message
   |       | was: trim(): Passing null to parameter #1 ($string) of type string is deprecated
   |       | in
   |       | /Users/stellarwp/Sites/orderable-website/wp-content/mu-plugins/stellarwp-web-common/stellarwp-web-common/vendor/wp-coding-standards/wpcs/WordPress/Sniffs/WP/I18nSniff.php
   |       | on line 194 (Internal.Exception)
------------------------------------------------------------------------------------------------

The line of code in I18nSniff.php that they mention is this:

// Allow overruling the text_domain set in a ruleset via the command line.
$cl_text_domain = trim( PHPCSHelper::get_config_data( 'text_domain' ) );

I was hoping there was a way we could fix this by reconfiguring how we were setting our text domain in our PHPCS XML config files, but the format we are using is correct:

<rule ref="WordPress.WP.I18n">
    <properties>
        <property name="text_domain" type="array">
            <element value="stellarwp-web-common"/>
        </property>
    </properties>
</rule>

Using a more up-to-date version of WPCS resolves this issue.