reticulate 1.27

• py_run_file() now ensures the __file__ dunder is visible to the
  executing python code. (#1283, #1284)

• Fixed errors with install_miniconda() and conda_install(),
  on Windows (#1286, #1287, conda/conda#11795, #1312, #1297),
  and on Linux and macOS (#1306, conda/conda#10431)

• Fixed error when activating a conda env from a UNC drive on Windows (#1303).