[master] Fix spelling errors

Produced via:
  `github.com/client9/misspell`
/assign ImJasonH vdemeester
/cc ImJasonH vdemeester

pkg/reconciler/pipelinerun/pipelinerun_test.go

@@ -980,7 +980,7 @@ func TestReconcileOnCompletedPipelineRun(t *testing.T) {
 	// TestReconcileOnCompletedPipelineRun runs "Reconcile" on a PipelineRun that already reached completion
 	// and that does not have the latest status from TaskRuns yet. It checks that the TaskRun status is updated
 	// in the PipelineRun status, that the completion status is not altered, that not error is returned and
-	// a succesful event is triggered
+	// a successful event is triggered
 	taskRunName := "test-pipeline-run-completed-hello-world"
 	prs := []*v1beta1.PipelineRun{tb.PipelineRun("test-pipeline-run-completed",
 		tb.PipelineRunNamespace("foo"),