Use built-in getExecOutput

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

__tests__/buildx.test.ts

@@ -1,6 +1,7 @@
 import * as fs from 'fs';
 import * as path from 'path';
 import * as semver from 'semver';
+import * as exec from '@actions/exec';
 
 import * as buildx from '../src/buildx';
 import * as context from '../src/context';
@@ -92,9 +93,26 @@ describe('isLocalOrTarExporter', () => {
   );
 });
 
+describe('isAvailable', () => {
+  const execSpy: jest.SpyInstance = jest.spyOn(exec, 'getExecOutput');
+  buildx.isAvailable();
+
+  expect(execSpy).toHaveBeenCalledWith(`docker`, ['buildx'], {
+    silent: true,
+    ignoreReturnCode: true
+  });
+});
+
 describe('getVersion', () => {
   async function isDaemonRunning() {
-    return await docker.isDaemonRunning();
+    return await exec
+      .getExecOutput(`docker`, ['version', '--format', '{{.Server.Os}}'], {
+        ignoreReturnCode: true,
+        silent: true
+      })
+      .then(res => {
+        return !res.stdout.includes(' ') && res.exitCode == 0;
+      });
   }
   (isDaemonRunning() ? it : it.skip)(
     'valid',