BUG: Fixed constant check regular expression

Author: Charles Marion

tests/library/PhpCheckstyle/config/default.cfg.xml

@@ -6,7 +6,7 @@
     <!--  ****************  -->
 
     <!-- Check Constant Naming -->
-    <test name="constantNaming" regexp="/^[A-Z_][A-Z_]*[A-Z_]$/" level="ERROR"/>
+    <test name="constantNaming" regexp="/^[A-Z0-9_][A-Z0-9_]*[A-Z0-9_]$/" level="ERROR"/>
 
     <!-- Check Variable Naming -->
     <test name="variableNaming" regexp="/^[a-zA-Z_][a-zA-Z0-9_]*$/" />