fix a bit on readme +1

README.md

@@ -27,7 +27,7 @@ class MyOneDice extends OneDice {
 
 ### Extend operator
 
-```
+```ts
 const onedice = new OneDice()
 onedice.addOperator(new Operator('+', 1, (a, [o, b]) => a + b))
 ```
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