fix get bash version and variable name

[danixmarques]

This merge fix the following error when installing marker with ~/.marker/install.py

Traceback (most recent call last):
  File "/home/daniel/javascript/./marker/install.py", line 97, in <module>
    main()
  File "/home/daniel/javascript/./marker/install.py", line 81, in main
    verify_requirements()
  File "/home/daniel/javascript/./marker/install.py", line 61, in verify_requirements
    m = re.search('(\d).(\d)', version_text)
  File "/usr/lib/python3.10/re.py", line 200, in search
    return _compile(pattern, flags).search(string)
TypeError: cannot use a string pattern on a bytes-like object

Also, fix a misspelled variable name.