html output failed for non-english enviroment

[dotnfc]

UnicodeDecodeError: 'gbk' codec can't decode byte 0xa6 in position 477: illegal multibyte sequence

it can be solved by (html/gen.py)
`
def generate_html_output(node_dict, title, custom_css=None):
table_content = ""

custom_css = custom_css or DEFAULT_CSS
with open(custom_css, encoding='utf-8') as f:
    css_styles = f.read()

with open(JAVASCRIPT, encoding='utf-8') as f:
    javascript = f.read()

... ...
`
open file with utf-8 encoding.

[Jędrzej Boczar]

Thanks