phraseTree引发的import error

[oasis-0927]

Describe the bug
python3.9+中将cgi.escape 移除，修改为html.escape ，新版本的nltk库中已经进行修改，但是由于本项目引用的是没有进行相关修改的phraseTree，因此在python 3.9+的环境中使用pretty_print方法会报错。

是否可以尝试将phraseTree都统一替换为nltk.tree 来解决此问题。

Code to reproduce the issue

import hanlp
from hanlp_common.document import Document


def merge_pos_into_con(doc: Document):
	flat = isinstancse(doc['pos'][0], str)
	if flat:
		doc = Document((k, [v]) for k, v in doc.items())
	for tree, tags in zip(doc['con'], doc['pos']):
		offset = 0
		for subtree in tree.subtrees(lambda t: t.height() == 2):
			tag = subtree.label()
			if tag == '_':
				subtree.set_label(tags[offset])
			offset += 1
	if flat:
		doc = doc.squeeze()
	return doc


con = hanlp.load('CTB9_CON_FULL_TAG_ELECTRA_SMALL')
tok = hanlp.load(hanlp.pretrained.tok.COARSE_ELECTRA_SMALL_ZH)
pos = hanlp.load(hanlp.pretrained.pos.CTB9_POS_ELECTRA_SMALL)
nlp = hanlp.pipeline().append(pos, input_key='tok', output_key='pos') \
	.append(con, input_key='tok', output_key='con')
doc = nlp(tok=["2021年", "HanLPv2.1", "带来", "最", "先进", "的", "多", "语种", "NLP", "技术", "。"])['con']
doc.pretty_print()

Describe the current behavior
A clear and concise description of what happened.

Expected behavior
A clear and concise description of what you expected to happen.

System information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04):
• Python version:3.10
• HanLP version:2.1.0b56

Other info / logs
Include any logs or source code that would be helpful to diagnose the problem. If including tracebacks, please include the full traceback. Large logs and files should be attached.

• • I've completed this form and searched the web for solutions.

[hankcs]

感谢反馈，已经修复，请检查上面的commit是否解决了这个问题。
如果还有问题，欢迎重开issue。

phrasetree有序列化的功能，而且更轻量化。

[oasis-0927]

测试已修复，感谢。