Project filter with datetime attribute name (i.e. project:scheduled) is parsed as project:

#### To report a bug...

* What command(s) did you run?
`task project:sch`
* What did you expect to happen?
For tasks with project `sch` to show.
```
ID Age Project Tag Due Description Urg
3 2d sch next 3d update/upgrade/backup laptop 30
14 1d sch 324 3d watch Racket/Haskell vids 15
```
* What actually happened?
Tasks without a project showed. When I reverted back to commit
8b4ae3b54 (v2.5.1), the output was as expected.
```
ID Age P Description Urg
11 1d H change gov. card addresses 6.01
26 10h setup Buku on phone 1
```
* Paste the output of the ```task diag``` command (v.2.6.0).
```
task 2.6.0
Platform: Linux

Compiler
Version: 9.1.0
Caps: +stdc +stdc_hosted +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++14

Build Features
Built: Sep 5 2019 11:39:46
Commit: cad8bec8b
CMake: 3.15.1
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.6.9
Build type: release

Configuration
File: /home/kevin/.taskrc (found), 2169 bytes, mode 100644
Data: /home/kevin/.task (found), dir, mode 40755
Locking: Enabled
GC: Enabled
$VISUAL: nvim
Server: taskd.khkm.tk:53589
CA: /home/kevin/.task/ca.cert.pem, readable, 3512 bytes
Certificate: /home/kevin/.task/do.cert.pem, readable, 3553 bytes
Key: /home/kevin/.task/do.key.pem, readable, 24742 bytes
Trust: strict
Ciphers: NORMAL
Creds: Hevin/Kevin/************************************

Hooks
System: Enabled
Location: /home/kevin/.task/hooks
Active:
Inactive: on-exit-auto-sync (not executable)

Tests
Terminal: 210x44
Dups: Scanned 51 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 51 tasks for broken references:
No broken references found

```
* Paste the output of the ```task diag``` command (v.2.5.1).
```
task 2.5.1
Platform: Linux

Compiler
Version: 9.1.0
Caps: +stdc +stdc_hosted +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++11

Build Features
Built: Sep 5 2019 11:48:01
Commit: 8b4ae3b54
CMake: 3.15.1
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.6.9
Build type: release

Configuration
File: /home/kevin/.taskrc (found), 2169 bytes, mode 100644
Data: /home/kevin/.task (found), dir, mode 40755
Locking: Enabled
GC: Enabled
$VISUAL: nvim
Server: taskd.khkm.tk:53589
CA: /home/kevin/.task/ca.cert.pem, readable, 3512 bytes
Trust: strict
Certificate: /home/kevin/.task/do.cert.pem, readable, 3553 bytes
Key: /home/kevin/.task/do.key.pem, readable, 24742 bytes
Ciphers: NORMAL
Creds: Hevin/Kevin/************************************

Hooks
System: Enabled
Location: /home/kevin/.task/hooks
Active:
Inactive: on-exit-auto-sync (not executable)

Tests
$TERM: screen-256color (210x44)
Dups: Scanned 51 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 51 tasks for broken references:
No broken references found
```