duplicate won't tell ID/UUID of newly created task

* What command(s) did you run?

task 30 duplicate

* What did you expect to happen?

Tell me the `ID` or `UUID` of the newly duplicated task.

* What actually happened?

task 30 duplicate
Note: task 30 was a parent recurring task. The duplicated task is too.
Duplicated task 30 'my task'.
Duplicated 1 task.

* Paste the output of the ```task diag``` command.

task 2.5.1
Platform: Linux

Compiler
Version: 7.2.0
Caps: +stdc +stdc_hosted +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++11

Build Features
CMake: 3.9.5
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.5.8
Build type: None

Configuration
[...]
Locking: Enabled
GC: Enabled
Server: naspi:53589
[...]
Hooks
System: Enabled
[...]
Tests
$TERM: xterm-256color (245x47)
Dups: Scanned 417 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 417 tasks for broken references:
No broken references found

#### To request a feature...

If this is not the intended behaviour of task, then it might be a feature request.

Anyhow, in the light of consistency, task should report the ID of tasks handled. Other task cmds do, this cmd (duplicate) for instance does not.

Might be related to: #331 #2085