Update phpcs.xml

This is specifically so that files like classes/CCR/DB/PDODB.php do not error.  If we decide to change at a later date we can remove this.

phpcs.xml

@@ -7,6 +7,7 @@
   <rule ref="PSR2">
       <exclude name="PSR2.Methods.FunctionCallSignature.SpaceBeforeCloseBracket" />
       <exclude name="PSR2.Methods.FunctionClosingBrace.SpacingBeforeClose" />
+      <exclude name="PSR2.Classes.PropertyDeclaration.Underscore" />
       <exclude name="PSR2.ControlStructures.ControlStructureSpacing.SpaceBeforeCloseBrace" />
       <exclude name="PSR2.ControlStructures.ControlStructureSpacing.SpacingAfterOpenBrace" />
       <exclude name="Squiz.Functions.MultiLineFunctionDeclaration.BraceOnSameLine" />