add ++= operator

Author: glcraft

syntaxes/nushell.tmLanguage.json

@@ -191,7 +191,7 @@
             "name": "keyword.control.nushell"
         },
         "operators-symbols": {
-            "match": "(?<= )(?:\\+|\\-|\\*|\\/|\\/\\/|\\*\\*|!=|[<>=]=?|[!=]~|&&|\\|\\||\\||\\+\\+)(?= |$)",
+            "match": "(?<= )(?:\\+|\\-|\\*|\\/|\\/\\/|\\*\\*|!=|[<>=]=?|[!=]~|&&|\\|\\||\\||\\+\\+=?)(?= |$)",
             "name": "keyword.control.nushell"
         },
         "operators": {