docs(typescript): update TS type import to new package name

[BBosman]

Description

Update the import in the Typescript docs to use the new @havesource/cordova-plugin-push package name.

Related Issue

n/a, just a small docs fix

Motivation and Context

When using the docs as-is, people will use the types from the previous package, which could even cause issues as that probably won't be installed.

How Has This Been Tested?

Successfully used that new import in my own project.

Screenshots (if appropriate):

n/a

Types of changes

• 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:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.