Update pcov unit test coverage config

Exclude AtoM's docker directory from pcov unit test coverage report. Add
pcov option to ensure all folders are scanned for unit test coverage
(plugin folder tests were not being discovered).

composer.json

@@ -30,7 +30,7 @@
     },
     "scripts": {
         "test": "phpunit",
-        "test-cov": "@php -dpcov.enabled=1 ./vendor/composer/bin/phpunit --coverage-html=.coverage/html",
+        "test-cov": "@php -dpcov.enabled=1 -dpcov.directory=. ./vendor/composer/bin/phpunit --coverage-html=.coverage/html",
         "php-cs-fixer": "php-cs-fixer"
     }
 }

phpunit.xml

@@ -12,6 +12,7 @@
       <directory suffix=".php">cache</directory>
       <directory suffix=".php">test</directory>
       <directory suffix=".php">vendor</directory>
+      <directory suffix=".php">docker</directory>
     </exclude>
   </coverage>
 </phpunit>