USWDS-Site - Documentation: Update `npm` References

[mahoneycm]

Summary

Updated npm references to all lowercase when not at the beginning of a sentence.

Breaking change

This is not a breaking change.

Related issue

Closes #2624

Preview link

Getting started for developers →

Maturity model →

Website policies and notices →

Problem statement

Where possible, avoid beginning sentences with words like "npm" that conventionally begin with a lowercase letter. When it appears at the beginning of a sentence, capitalize the N in npm.

See this conversation in Slack for more context (🔒) on the decision about why to capitalize the N in npm at the beginning of a sentence.

Solution

Update all documentation references of npm to match the preferred pattern.

[!NOTE] The documentation page content is pulled directly from the USWDS README. These npm references will be updated as a part of uswds/uswds#5915

Testing and review

1. Inspect the following pages and confirm all references to npm match the expected pattern
   1. Getting started for developers
   2. Maturity model
   3. Website policies and notices
2. Confirm there are no additional references to npm that need to be updated
3. Approve of additional changelogs

For Devs

1. Use VSCode search with Match case and match whole world to ensure there are no other references of npm that do not match the expected pattern