Importing modifications to a child recurring task does not update parent task

* What command(s) did you run?
```
> task import
{ "description": "test", "due": "20300801T070000Z", "uuid": "ab030565-fc46-4ef2-bfd3-bdd2b840dbfa", "status": "pending", "recur": "weekly"}
> task export (note uuid of child for next command)
> task rc.recurrence.confirmation=yes import
{"id":2,"description":"test2","due":"20300801T070000Z","entry":"20200722T145853Z","imask":0,"parent":"ab030565-fc46-4ef2-bfd3-bdd2b840dbfa","recur":"weekly","status":"pending","uuid":"ca11f061-94a1-4cc2-8577-85c73016b596"}
```

* What did you expect to happen?

I expected the parent task to be modified so its description becomes `test2`.

* What actually happened?

The parent task was not changed in any way.

* Paste the output of the ```task diag``` command.
```
task 2.5.1
Platform: Darwin

Compiler
Version: 4.2.1 Compatible Apple LLVM 11.0.0 (clang-1100.0.33.8)
Caps: +stdc +stdc_hosted +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++11

Build Features
Built: Oct 16 2019 19:08:34
CMake: 3.15.4
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.6.10
Build type: Release

Configuration
File: /Users/dave/testtask/taskrc (found), 3825 bytes, mode 100644
Data: /Users/dave/testtask/tasks (found), dir, mode 40755
TASKRC: /Users/dave/testtask/taskrc
Locking: Enabled
GC: Enabled
$VISUAL: code -w
Server:
Trust: strict
Certificate: , not readable, 0 bytes
Key: , not readable, 0 bytes
Ciphers: NORMAL
Creds:

Hooks
System: Enabled
Location: /Users/dave/testtask/tasks/hooks
(-none-)

Tests
$TERM: xterm-256color (316x74)
Dups: Scanned 2 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 2 tasks for broken references:
No broken references found
```