Fix CS error

Author: ADmad

src/Plugin.php

@@ -259,9 +259,9 @@ public function getPrimaryNamespace(PackageInterface $package): string
         if (!$primaryNs) {
             throw new RuntimeException(
                 sprintf(
-                    "Unable to get primary namespace for package %s." .
+                    'Unable to get primary namespace for package %s.' .
                     "\nEnsure you have added proper 'autoload' section to your plugin's config" .
-                    " as stated in README on https://github.com/cakephp/plugin-installer",
+                    ' as stated in README on https://github.com/cakephp/plugin-installer',
                     $package->getName()
                 )
             );