docs: fix arg separator

Author: fknop

docs/string.md

@@ -397,18 +397,18 @@ import { WithPipe } from 'angular-pipes';
 ##### Usage
 
 ```html
-{{'The Flash Reverse' | with: 'The',null, true}} <!-- result: true -->
-{{'The Flash Reverse' | with: 'The','Reverse',true}} <!-- result: true-->
-{{'The Flash Reverse' | with: 'The','Reverse'}} <!-- result: true-->
-{{'The Flash Reverse' | with: 'the','reverse'}} <!-- result: true-->
-{{'The Flash Reverse' | with: 'the','Reverse',true}} <!-- result: false-->
-{{'The Flash Reverse' | with: 'the','reverse',true}} <!-- result: false-->
-{{'The Flash Reverse' | with: 'Blue','Reverse',true}} <!-- result: false-->
-{{'The Flash Reverse' | with: 'The','Black',true}} <!-- result: false-->
-{{'The Flash Reverse' | with: '','Black',true}} <!-- result: false-->
-{{'The Flash Reverse' | with: '','',true}} <!-- result: 'The Flash Reverse'-->
-{{'The Flash Reverse' | with: null,null,true}} <!-- result: 'The Flash Reverse'-->
-{{'The Flash Reverse' | with: null,null}} <!-- result: 'The Flash Reverse'-->
+{{'The Flash Reverse' | with: 'The' : null, true}} <!-- result: true -->
+{{'The Flash Reverse' | with: 'The' : 'Reverse' : true}} <!-- result: true-->
+{{'The Flash Reverse' | with: 'The' : 'Reverse'}} <!-- result: true-->
+{{'The Flash Reverse' | with: 'the' : 'reverse'}} <!-- result: true-->
+{{'The Flash Reverse' | with: 'the' : 'Reverse' : true}} <!-- result: false-->
+{{'The Flash Reverse' | with: 'the' : 'reverse' : true}} <!-- result: false-->
+{{'The Flash Reverse' | with: 'Blue' : 'Reverse' : true}} <!-- result: false-->
+{{'The Flash Reverse' | with: 'The' : 'Black' : true}} <!-- result: false-->
+{{'The Flash Reverse' | with: '' : 'Black' : true}} <!-- result: false-->
+{{'The Flash Reverse' | with: '' : '' : true}} <!-- result: 'The Flash Reverse'-->
+{{'The Flash Reverse' | with: null : null : true}} <!-- result: 'The Flash Reverse'-->
+{{'The Flash Reverse' | with: null : null}} <!-- result: 'The Flash Reverse'-->
 {{'The Flash Reverse' | with}} <!-- result: 'The Flash Reverse'-->
 ```