build_utils: Start using pip 20.3.4 instead of 10.0.0

build_utils: Start using pip 20.3.4 instead of 10.0.0

Started seeing
```
+ /tmp/venv.ivc8u2qcCO/bin/pip install --no-binary=:all: --upgrade --exists-action=i --find-links=file:///home/jenkins-build/.cache/pip --no-index 'jenkins-job-builder>=3.5.0'
Looking in links: file:///home/jenkins-build/.cache/pip
Collecting jenkins-job-builder>=3.5.0
Collecting six>=1.9.0 (from jenkins-job-builder>=3.5.0)
Collecting PyYAML<6,>=3.10.0 (from jenkins-job-builder>=3.5.0)
  Could not find a version that satisfies the requirement wheel (from versions: )
No matching distribution found for wheel
```

Even 21.0.1 on Ubuntu 16.04 was failing.  It's just time to pin a newer version.

Signed-off-by: David Galloway <dgallowa@redhat.com>