fix: QStepper next check for last step and unused flat property (quasarframework#617)

* fix: QStepper next check for last step and unused flat property

* fix: QStepper - typo

* fix: QStepper duplicate step-error class

Author: pdanpdan

src/components/stepper/QStepper.vue

@@ -114,7 +114,7 @@ export default {
     },
     reset () {
       if (this.hasSteps) {
-        this.gotToStep(this.steps[0].name)
+        this.goToStep(this.steps[0].name)
       }
     },
 

src/components/stepper/StepTab.vue

@@ -5,7 +5,6 @@
       'step-error': vm.error,
       'step-active': vm.active,
       'step-done': vm.done,
-      'step-error': vm.error,
       'step-waiting': vm.waiting,
       'step-disabled': vm.disable,
       'step-colored': vm.active || vm.done,