Missing process for formatting.blackPath

[MisLink]

Environment data

• VS Code version: 1.25.1
• Extension version (available under the Extensions sidebar): 2018.7.1
• OS and version: macOS 10.13.6
• Python version (& distribution if applicable, e.g. Anaconda): CPython 3.6.6
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): venv
• Relevant/affected Python packages and their versions: black

Actual behavior

I tried to use ~/.local/bin/black as path to the black but vscode prompted me that "Path to the black formatter is invalid". It's kind of weird because my flake8 is on the same path but it works just fine. And I found there's a missing process for blackPath on https://github.com/Microsoft/vscode-python/blob/master/src/client/common/configSettings.ts#L231-L233 .

Expected behavior

expand user home directory.

Steps to reproduce:

1. set formatting.blackPath under a user home directory and use "~"
2. try to format a file

Logs

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

XXX

Output from Console under the Developer Tools panel (toggle Developer Tools on under Help)

XXX

[DonJayamanne]

Closing in favor of #2274