bug(pip): pip in Windows is now called via py

Instead of the incorrect `python3`

CHANGELOG.md

@@ -49,6 +49,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+- Changed the way Python is invoked in Windows machines uses `py` instead of `python`
 - Changed the `npm vsce` package to `@vscode/vsce` for publishing
   ([#814](https://github.com/fortran-lang/vscode-fortran-support/issues/814))
 - Changed logger to draw focus on certain error messages

src/lib/tools.ts

@@ -4,6 +4,7 @@ import * as vscode from 'vscode';
 import * as assert from 'assert';
 import * as cp from 'child_process';
 import { isString, isArrayOfString } from './helper';
+import { off } from 'process';
 
 export const LS_NAME = 'fortls';
 export const EXTENSION_ID = 'fortran';
@@ -142,7 +143,10 @@ export async function promptForMissingTool(
  * @param pyPackage name of python package in PyPi
  */
 export async function pipInstall(pyPackage: string): Promise<string> {
-  const py = 'python3'; // Fetches the top-most python in the Shell
+  let py = 'python3'; // Fetches the top-most python in the Shell
+  // For Windows, use py instead of python3, see:
+  // https://packaging.python.org/en/latest/tutorials/installing-packages/#installing-from-pypi
+  if (process.platform === 'win32') py = 'py';
   const args = ['-m', 'pip', 'install', '--user', '--upgrade', pyPackage];
   return await shellTask(py, args, `pip: ${pyPackage}`);
 }