Refactor install dir computation

src/utils.ts

@@ -1,2 +1,7 @@
 export const IS_WINDOWS = process.platform === 'win32';
 export const IS_LINUX = process.platform === 'linux';
+export const getPlatform = (): 'windows' | 'linux' | 'mac' => {
+  if (IS_WINDOWS) return 'windows';
+  if (IS_LINUX) return 'linux';
+  return 'mac';
+};