Avoid Windows crashes when wmic is not available

Previously this code didn't actually listen for the result of
the command at all, assuming incorrectly that it was a promise.
Now it properly waits until the process closes, and watches
for errors.

Author: pimterry

src/interceptors/fresh-firefox.ts

@@ -171,7 +171,7 @@ export class FreshFirefox implements Interceptor {
             if (process.platform === "win32") {
                 // Firefox spawns a child process on Windows, and doesn't let us kill it at all.
                 // To fix this, we kill all firefox instances that were started with this exact same URL.
-                await windowsKill(`CommandLine Like '%\\\\firefox.exe%${initialUrl}'`);
+                await windowsKill(`CommandLine Like '%\\\\firefox.exe%${initialUrl}'`).catch(console.log);
             } else {
                 normalStop();
             }

src/util.ts

@@ -47,13 +47,11 @@ export function getDeferred<T = void>(): Deferred<T> {
 }
 
 export async function windowsKill(processMatcher: string) {
-    await spawn('wmic', [
+    await spawnToResult('wmic', [
         'Path', 'win32_process',
         'Where', processMatcher,
         'Call', 'Terminate'
-    ], {
-        stdio: 'inherit'
-    });
+    ], { }, true);
 }
 
 // Spawn a command, and resolve with all output as strings when it terminates