Actually use executablePath setting

src/extension.ts

@@ -51,7 +51,7 @@ export async function activate(context: vscode.ExtensionContext): Promise<void>
         function spawnServer(...args: string[]): ChildProcess {
             // The server is implemented in PHP
             args.unshift(context.asAbsolutePath(path.join('vendor', 'felixfbecker', 'language-server', 'bin', 'php-language-server.php')));
-            const childProcess = spawn('php', args);
+            const childProcess = spawn(executablePath, args);
             childProcess.stderr.on('data', (chunk: Buffer) => {
                 console.error(chunk + '');
             });