ci_addons --install: Do not copy *.pyc files

[jcfr]

I suggest to not install *.pyc files. It currently does:

python.exe -m ci_addons --install ..
C:\projects\anyci\noop.py
C:\projects\anyci\noop.pyc
C:\projects\anyci\run.sh
C:\projects\anyci\__init__.pyc
C:\projects\appveyor\apply_mingw_path_fix.py
C:\projects\appveyor\apply_mingw_path_fix.pyc
C:\projects\appveyor\enable-worker-remote-access.ps1
C:\projects\appveyor\install_cmake.py
C:\projects\appveyor\install_cmake.pyc
C:\projects\appveyor\patch_vs2008.py
C:\projects\appveyor\patch_vs2008.pyc
C:\projects\appveyor\rolling-build.ps1
C:\projects\appveyor\run-with-mingw.cmd
C:\projects\appveyor\run-with-visual-studio.cmd
C:\projects\appveyor\run.cmd
C:\projects\appveyor\tweak_environment.py
C:\projects\appveyor\tweak_environment.pyc
C:\projects\appveyor\__init__.pyc
C:\projects\circle\install_cmake.py
C:\projects\circle\install_cmake.pyc
C:\projects\circle\__init__.pyc
C:\projects\travis\install_cmake.py
C:\projects\travis\install_cmake.pyc
C:\projects\travis\install_pyenv.py
C:\projects\travis\install_pyenv.pyc
C:\projects\travis\run-with-pyenv.sh
C:\projects\travis\__init__.pyc