Bump version to 0.1.8 and fix typo in contract password

[ehsan-fj]

This pull request mainly addresses a typo in the contact creation XML template constant, updates references throughout the codebase, and bumps the package version. The changes ensure naming consistency and improve code readability.

Version bump:

• Updated the package version from 0.1.7 to 0.1.8 in pyepp/__init__.py.

Naming consistency and typo fixes:

• Renamed the constant CONTACT_CREAT_XML to CONTACT_CREATE_XML in pyepp/command_templates.py to fix a typo.
• Updated all references from CONTACT_CREAT_XML to CONTACT_CREATE_XML in pyepp/contact.py. [1] [2]
• Remove an extra space from <contact:pw> tag in CONTACT_CREATE_XML

Code readability:

• Reformatted the assignment for address_change in the update method of pyepp/contact.py for better readability.