🔥 suppress pip install output. #378

[chfw]

Before raising the PR, here is a check list:

• have you written unit tests for your code changes?
• have you updated the change log?
• can someone else understand your changes without your explanation?
• are you proud of your code changes?
• please add your name and github link to contributors.rst in alphabetical order.

[codecov-io]

Codecov Report

Merging #379 into dev will increase coverage by 0.00%.
The diff coverage is 93.33%.

@@           Coverage Diff           @@
##              dev     #379   +/-   ##
=======================================
  Coverage   96.05%   96.05%           
=======================================
  Files          55       55           
  Lines        2866     2868    +2     
=======================================
+ Hits         2753     2755    +2     
  Misses        113      113           

Impacted Files	Coverage Δ
moban/core/moban_factory.py	98.10% <ø> (ø)
moban/deprecated/__init__.py	86.36% <ø> (ø)
moban/plugins/jinja2/engine.py	100.00% <ø> (ø)
tests/test_file_system.py	95.52% <ø> (ø)
moban/externals/reporter.py	96.07% <91.66%> (+0.16%)	⬆️
moban/_version.py	100.00% <100.00%> (ø)
...sts/integration_tests/test_command_line_options.py	99.40% <100.00%> (ø)

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