Replace "whitelist" with "allowlist" in example

This term is more descriptive, IMO. Also, [less contentious](https://tools.ietf.org/id/draft-knodel-terminology-00.html#rfc.section.1.2).

doc/statuscodes.md

@@ -10,7 +10,7 @@ statuses are defined as such:
 | UNKNOWN | 2 | Unknown error. For example, this error may be returned when a `Status` value received from another address space belongs to an error space that is not known in this address space. Also errors raised by APIs that do not return enough error information may be converted to this error. |
 | INVALID_ARGUMENT | 3 | The client specified an invalid argument. Note that this differs from `FAILED_PRECONDITION`. `INVALID_ARGUMENT` indicates arguments that are problematic regardless of the state of the system (e.g., a malformed file name). |
 | DEADLINE_EXCEEDED | 4 | The deadline expired before the operation could complete. For operations that change the state of the system, this error may be returned even if the operation has completed successfully. For example, a successful response from a server could have been delayed long |
-| NOT_FOUND | 5 | Some requested entity (e.g., file or directory) was not found. Note to server developers: if a request is denied for an entire class of users, such as gradual feature rollout or undocumented whitelist, `NOT_FOUND` may be used. If a request is denied for some users within a class of users, such as user-based access control, `PERMISSION_DENIED` must be used. |
+| NOT_FOUND | 5 | Some requested entity (e.g., file or directory) was not found. Note to server developers: if a request is denied for an entire class of users, such as gradual feature rollout or undocumented allowlist, `NOT_FOUND` may be used. If a request is denied for some users within a class of users, such as user-based access control, `PERMISSION_DENIED` must be used. |
 | ALREADY_EXISTS | 6 | The entity that a client attempted to create (e.g., file or directory) already exists. |
 | PERMISSION_DENIED | 7 | The caller does not have permission to execute the specified operation. `PERMISSION_DENIED` must not be used for rejections caused by exhausting some resource (use `RESOURCE_EXHAUSTED` instead for those errors). `PERMISSION_DENIED` must not be used if the caller can not be identified (use `UNAUTHENTICATED` instead for those errors). This error code does not imply the request is valid or the requested entity exists or satisfies other pre-conditions. |
 | UNAUTHENTICATED | 16 | The request does not have valid authentication credentials for the operation. |