Misspell correction (#826)

Did a `misspell . | grep -v ^vendor` and fixed
several typos.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

middleware/kubernetes/kubernetes_test.go

@@ -71,7 +71,7 @@ func TestIsNameError(t *testing.T) {
 	if !k.IsNameError(errInvalidRequest) {
 		t.Errorf("Expected 'true' for '%v'", errInvalidRequest)
 	}
-	otherErr := errors.New("Some other error occured")
+	otherErr := errors.New("Some other error occurred")
 	if k.IsNameError(otherErr) {
 		t.Errorf("Expected 'true' for '%v'", otherErr)
 	}