Add missing locale

Author: mtoffl01

internal-api/src/main/java/datadog/trace/bootstrap/config/provider/StableConfigParser.java

@@ -142,8 +142,8 @@ static boolean selectorMatch(String origin, List<String> matches, String operato
     if (operator == null) {
       return false;
     }
-    operator = operator.toLowerCase();
-    switch (origin.toLowerCase()) {
+    operator = operator.toLowerCase(Locale.ROOT);
+    switch (origin.toLowerCase(Locale.ROOT)) {
       case "language":
         if ("exists".equals(operator)) {
           return false;