Typo in pythonPath setting name

Commit https://github.com/Microsoft/vscode-python/commit/6c80bbc71c4f7354e2eed4c4db4756373cb43e3d#diff-fe6cc817f22d2e970137cec7306be6a3R325 introduced a typo in the `pythonPath` setting name. (just noticed this while looking at source code, but I'm sure it will cause bugs :smile:)

PR with fix: #3991