JS: add change note

Author: asger-semmle

change-notes/1.20/analysis-javascript.md

@@ -13,6 +13,7 @@
 | Double escaping or unescaping (`js/double-escaping`) | correctness, security, external/cwe/cwe-116 | Highlights potential double escaping or unescaping of special characters, indicating a possible violation of [CWE-116](https://cwe.mitre.org/data/definitions/116.html). Results are shown on LGTM by default. |
 | Incomplete URL substring sanitization | correctness, security, external/cwe/cwe-020 | Highlights URL sanitizers that are likely to be incomplete, indicating a violation of [CWE-020](https://cwe.mitre.org/data/definitions/20.html). Results shown on LGTM by default. |
 | Incorrect suffix check (`js/incorrect-suffix-check`) | correctness, security, external/cwe/cwe-020 | Highlights error-prone suffix checks based on `indexOf`, indicating a potential violation of [CWE-20](https://cwe.mitre.org/data/definitions/20.html). Results are shown on LGTM by default. |
+| Missing index adjustment after concurrent modification (`js/missing-index-adjustment-after-concurrent-modification`) | correctness | Highlights code that removes an element from an array while iterating over it, causing the loop to skip over some elements. Results are shown on LGTM by default. |
 | Useless comparison test (`js/useless-comparison-test`) | correctness | Highlights code that is unreachable due to a numeric comparison that is always true or always false. Results are shown on LGTM by default. |
 
 ## Changes to existing queries