Update the license keys of the ABOUT file from 'license' to 'license_expression' and 'license_text_file' to 'license_file'

[chinyeungli]

See https://github.com/aboutcode-org/aboutcode-toolkit/blob/develop/src/attributecode/model.py#L900 for the current supported keys.

https://github.com/aboutcode-org/python-publicsuffix2/blob/develop/src/publicsuffix2/public_suffix_list.ABOUT#L10

Current

about_resource: public_suffix_list.dat
name: Public Suffix List
version: 2020-01-27T10:24:28
download_url: https://publicsuffix.org/list/public_suffix_list.dat
home_url: https://publicsuffix.org/

owner: Mozilla
copyright: Copyright (c) Mozilla and others
license: mpl-2.0
license_text_file: mpl-2.0.LICENSE

Porposed

about_resource: public_suffix_list.dat
name: Public Suffix List
version: 2020-01-27T10:24:28
download_url: https://publicsuffix.org/list/public_suffix_list.dat
home_url: https://publicsuffix.org/

owner: Mozilla
copyright: Copyright (c) Mozilla and others
license_expression: mpl-2.0
license_file: mpl-2.0.LICENSE