Revert error exit change

Author: KaiPrince

src/lib/runner.js

@@ -70,7 +70,7 @@ class Runner {
 
       this.childProcess.on('close', (code) => {
         if (code !== 0) {
-          reject(code);
+          reject(this.#stdErrBuffer);
           return;
         }
         resolve();

test/cases/runner-cli-error/runner-cli-error.spec.js

@@ -46,9 +46,7 @@ describe('CLI Error Handling', function() {
         runner.runCommand(
           path.join(process.cwd(), 'test/fixtures/cli-promise-rejection.js'),
         )
-      ).to.be.rejectedWith(1)
-
-      expect(runner.getStdErr()).to.include(
+      ).to.be.rejectedWith(
         'Error: Child process throwing a Promise.reject to the parent.',
       );
     });