Thresholds.md javascript codeblocks adds (#1274)

* Thresholds.md javascript codeblocks adds

* Update 04 Thresholds.md

Author: mstoykov

src/data/markdown/translated-guides/en/02 Using k6/04 Thresholds.md

@@ -75,17 +75,18 @@ and k6 would exit with a non-zero exit code.
 To use a threshold, follow these steps:
 
 1. In the `thresholds` property of the `options` object, set a key using the name of the metric you want the threshold for:
-  ```
+  ```javascript
   export const options = {
     thresholds: {
-    ...
+      /* ... */
+    }
   }
   ```
 2. Define at least one threshold expression. You can do this in two ways:
     - The short format puts all threshold expressions as strings in an array.
     - The long format puts each threshold in an object, with extra properties to [abort on failure](#abort).
 
-  ```
+  ```javascript
   export const options = {
     thresholds: {
       //short format