Update .phpcs.xml: Check $PWD by default

.phpcs.xml

@@ -5,6 +5,11 @@
         but without the MissingNamespace sniff.
     </description>
 
+    <!--
+        Run on current working directory by default
+    -->
+    <file>.</file>
+
     <!--
         Exclude _build/ and vendor/ dirs as well as minified JavaScript files
     -->