use correct variable name

[knoxell]

Description

• [ x ] Source branch in your fork has meaningful name (not main)

Fixes Issue:

beautify_file of cssbeautifier (python module) not working because usage of two different variable names file and file_name.

See __init__.py:

...
def beautify_file(file_name, opts=None):
    _main = __import__("cssbeautifier", globals(), locals(), ["_main"])._main
    return _main.beautify_file(file, opts)
...

results in:

# file.py
import cssbeautifier

cssbeautifier.beautify_file('./file.css')

$ python file.py         
Traceback (most recent call last):
  File ".../file.py", line 3, in <module>
    x = cssbeautifier.beautify_file('./file.css')
  File ".../cssbeautifier/__init__.py", line 41, in beautify_file
    return _main.beautify_file(file, opts)
NameError: name 'file' is not defined. Did you mean: 'filter'?

Before Merge Checklist

These items can be completed after PR is created.

(Check any items that are not applicable (NA) for this PR)

• [ x ] JavaScript implementation
• Python implementation (NA if HTML beautifier)
• [ x ] Added Tests to data file(s)
• [ x ] Added command-line option(s) (NA if
• [ x ] README.md documents new feature/option(s)