Change PLATFORM to constant instead of function

src/installer.ts

@@ -7,7 +7,7 @@ import {chmodSync} from 'fs';
 import path from 'path';
 import os from 'os';
 import semver from 'semver';
-import {IS_WINDOWS, getPlatform} from './utils';
+import {IS_WINDOWS, PLATFORM} from './utils';
 import {QualityOptions} from './setup-dotnet';
 
 export interface DotnetVersion {
@@ -223,7 +223,7 @@ export abstract class DotnetInstallDir {
     ? DotnetInstallDir.convertInstallPathToAbsolute(
         process.env['DOTNET_INSTALL_DIR']
       )
-    : DotnetInstallDir.default[getPlatform()];
+    : DotnetInstallDir.default[PLATFORM];
 
   private static convertInstallPathToAbsolute(installDir: string): string {
     if (path.isAbsolute(installDir)) return path.normalize(installDir);

src/utils.ts

@@ -1,7 +1,6 @@
 export const IS_WINDOWS = process.platform === 'win32';
-export const IS_LINUX = process.platform === 'linux';
+export const PLATFORM = ((): 'windows' | 'linux' | 'mac' => {
-export const getPlatform = (): 'windows' | 'linux' | 'mac' => {
+  if (process.platform === 'win32') return 'windows';
-  if (IS_WINDOWS) return 'windows';
+  if (process.platform === 'linux') return 'linux';
-  if (IS_LINUX) return 'linux';
   return 'mac';
-};
+})();