Update django-pipeline to latest #2689

[phillxnet]

Remove version pinning given we have now removed
the prior dual constraint re Python version and
Django version.

Fixes #2689

[phillxnet]

Testing

An rpm was built successfully, so all tests passed, using a Leap 15.5/amd64 base; from the product of this PR. This RPM installed successfully with the expected zypper history log entries re static files creation e.g.:

...
# Post-processed 'storageadmin/css/style.css' as 'storageadmin/css/style.f4d53bb84d12.css'
# Post-processed 'rest_framework/css/bootstrap-theme.min.css' as 'rest_framework/css/bootstrap-theme.min.66b84a04375e.css'
# Post-processed 'rest_framework/css/bootstrap-tweaks.css' as 'rest_framework/css/bootstrap-tweaks.46ed116b0edd.css'
# Post-processed 'rest_framework/css/bootstrap.min.css' as 'rest_framework/css/bootstrap.min.77017a69879a.css'
# Post-processed 'rest_framework/css/default.css' as 'rest_framework/css/default.8d5591a6aabc.css'
# Post-processed 'rest_framework/css/font-awesome-4.0.3.css' as 'rest_framework/css/font-awesome-4.0.3.c1e1ea213abf.css'
# Post-processed 'rest_framework/css/prettify.css' as 'rest_framework/css/prettify.a987f72342ee.css'
# 
# 506 static files copied to '/opt/rockstor/static', 576 post-processed.
# 
# ROCKSTOR BUILD SCRIPT COMPLETED

The resulting install was setup via Web-UI and appeared as expected. A Web-UI development mode network disable-cache was also used to ensure the newly generated static files were those in play.

[phillxnet]

Popping this on in as looks to be fairly safe.