Updated more referencs to constants

regex/compile.go

@@ -768,7 +768,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 			// Keep popping from opStack until we encounter an opening parantheses or a NONCAPLPAREN_CHAR. Throw error if we reach the end of the stack.
 			var val rune
 			var err error
-			for val, err = peek(opStack); val != '(' && val != NONCAPLPAREN_CHAR; val, err = peek(opStack) {
+			for val, err = peek(opStack); val != '(' && val != nonCapLparenRune; val, err = peek(opStack) {
 				if err != nil {
 					return nil, fmt.Errorf("imbalanced parantheses")
 				}