HashMap Data Structure: Update introduction paragraph

[ruizterce]

Because

Clarifies what HashMaps are and why are they useful before diving into the lesson.

This PR

• Updates introductory paragraph of HashMap Data Structure lessons in Ruby and JavaScript paths.

Issue

Closes #29313

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[JoshDevHub]

A couple small corrections just so we stay consistent with the term "hash map" (space between words throughout the lesson, but used as one word in your changes).

More my fault than yours since I spelled it with one word in the issue. But yeah, as soon as you can get that committed, I'll be good to approve and merge.

[ruizterce]

My apologies, I should've caught that! Thanks for the review, I just committed your suggested changes.