Typo in the select Python interpreter balloon for macOS

[joe-graham]

I can submit a pull request for this momentarily since this is a one-word cosmetic issue.

Environment data

• VS Code version: 1.28.0
• Extension version (available under the Extensions sidebar): 2018.9.0
• OS and version: macOS Mojave (10.14)
• Python version (& distribution if applicable, e.g. Anaconda): 3.7.0
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): N/A
• Relevant/affected Python packages and their versions: N/A

Actual behavior

The balloon that pops up when installing the extension for the first time says "You have selected the macOS system install of Python, which is not not recommended for use with the Python extension."

Expected behavior

This should instead say: "You have selected the macOS system install of Python, which is not recommended for use with the Python extension."

Steps to reproduce:

1. Install the extension for the first time on a macOS system, while having an additional version of Python installed via Homebrew.
2. Open any Python file.

Logs

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

N/A

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

N/A