tensorlayerx没有优化函数的基类， 只能使用tlx.optimizers.paddle_optimizers.Optimizer来判断

[zhxiucui]

New Issue Checklist

• I have read the Contribution Guidelines
• I searched for existing GitHub issues

Issue Description

[INSERT DESCRIPTION OF THE PROBLEM]

Reproducible Code

• Which OS are you using ?
• Please provide a reproducible code of your issue. Without any reproducible code, you will probably not receive any help.

[INSERT CODE HERE]

# ======================================================== #
###### THIS CODE IS AN EXAMPLE, REPLACE WITH YOUR OWN ######
# ======================================================== #
# paddle
import paddle
x = 13
print(isinstance(x, paddle.optimizers.Optimizer))

# tensorlayer
import os
os.environ['TL_BACKEND'] = 'paddle'
import tensorlayer as tlx
x = 13
print(isinstance(x, tlx.optimizers.paddle_optimizers.Optimizer))
# ======================================================== #
###### THIS CODE IS AN EXAMPLE, REPLACE WITH YOUR OWN ######
# ======================================================== #