Update for liquidprompt theme v2.0 support

When using the theme liquidprompt v2.0 or later with bash-it, bash issues an error message when the prompt is displayed with the current working directory in a git repository that is not in detached head state.

Description

In v2.0 (released Feb 5, 2021) of liquidprompt, the function _lp_escape() was renamed to __lp_escape(). Therefore, calling the function by the old name results in an error message from bash. By using the new name, the problem goes away.

The shim used by bash-it still uses the old name.

Motivation and Context

The annoying error message goes away with this change.

How Has This Been Tested?

Change made. Issued bash-it reload. Error message no longer appears.

Screenshots (if appropriate):

Types of changes

[X] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[X] My code follows the code style of this project.
[X] If my change requires a change to the documentation, I have updated the documentation accordingly.
[X] I have read the CONTRIBUTING document.
[ ] If I have added a new file, I also added it to clean_files.txt and formatted it using lint_clean_files.sh.
[ ] I have added tests to cover my changes, and all the new and existing tests pass.

Bash-it / bash-it