CDRIVER-2774 update change stream example

Author: kevinAlbs

src/libmongoc/tests/test-mongoc-sample-commands.c

@@ -2607,17 +2607,15 @@ test_example_change_stream (mongoc_database_t *db)
                         "{",
                         "$match",
                         "{",
-                        "$or",
-                        "[",
-                        "{",
                         "fullDocument.username",
                         BCON_UTF8 ("alice"),
                         "}",
-                        "{",
-                        "operationType",
-                        BCON_UTF8 ("delete"),
                         "}",
-                        "]",
+                        "{",
+                        "$addFields",
+                        "{",
+                        "newField",
+                        BCON_UTF8 ("this is an added field!"),
                         "}",
                         "}",
                         "]");