fixed issue which caused always using yarn as the packager

setup.js

@@ -9,31 +9,29 @@ const devDependencies = require('./devDependencies.json');
 const deleteFile = (fileName) => fs.unlinkSync(path.join(process.cwd(), fileName));
 const writeFile = (fileName, data) => fs.writeFileSync(path.join(process.cwd(), fileName), data);
 const isYarnAvailable = () => {
-  try {
-    execSync('yarnpkg --version', { stdio: 'ignore' });
-    return true;
-  } catch (e) {
-    return false;
-  }
-}
-const currPackager = isYarnAvailable ? "yarn" : "npm";
-const logInstallingWith = pkg => console.log(`\n📦 Installing dependencies with ${pkg}...\n`);
-const execOptions = {
-  stdio: 'inherit'
+    try {
+        execSync('yarnpkg --version', { stdio: 'ignore' });
+        return true;
+    } catch (e) {
+        return false;
+    }
 }
 
+const packager = isYarnAvailable() ? 'yarn' : 'npm';
+const execOptions = { stdio: 'inherit' };
+
 console.log('\n🔄 Please wait...\n');
 
 packageJson.scripts.start = `${packageJson.scripts.start} --config ../../../../rn-cli.config.js`;
 packageJson.jest = Object.assign(packageJson.jest, jestJson);
 writeFile('package.json', JSON.stringify(packageJson, null, 2));
 
-logInstallingWith(currPackager);
+console.log(`\n📦 Installing dependencies with ${packager}...\n`);
 
-if (isYarnAvailable) {
-  execSync(`yarn add ${devDependencies.join(' ')} --dev --exact`, execOptions);
+if (packager === 'yarn') {
+    execSync(`yarn add ${devDependencies.join(' ')} --dev --exact`, execOptions);
 } else {
-  execSync(`npm i ${devDependencies.join(' ')} --save-dev --save-exact`, execOptions);
+    execSync(`npm i ${devDependencies.join(' ')} --save-dev --save-exact`, execOptions);
 }
 
 deleteFile('App.js');
@@ -45,4 +43,4 @@ deleteFile('README.md');
 deleteFile('LICENSE');
 deleteFile('setup.js');
 
-console.log(`\n✅ Setup completed! You can now start with: ${currPackager} start\n`);
+console.log(`\n✅ Setup completed! You can now start with: ${packager} start\n`);