Fix typos

[sankichi92]

Related Issue(s):

#1163 is related PR.

Proposed Changes:

1. Fix typos in best-practices.md
   1. Remove unnecessary is

      • The best practice is to use as specific of a media type as is possible

   2. Fix typo the => that

      • The ones the that say Item Spec are the only 'official' roles that are fully standardized

2. Remove repeated the
   • I confirmed there are no repeated the anymore by searching the the in this repository.

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes.
• I have added my changes to the CHANGELOG
  or a CHANGELOG entry is not required.
• This PR affects the STAC API spec,
  and I have opened issue/PR #XXX to track the change.

[sankichi92]

CircleCI Pipeline failed, but it it not relevant to my changes:

Could not find a usable config.yml, you may have revoked the CircleCI OAuth app.
Please sign out of CircleCI and log back in with your VCS before triggering a new pipeline.

Could you confirm GitHub integration settings?

[sankichi92]

Thank you for approval, but I found another typo (repeated "the") and added a commit.

And I logged in CircleCI with my GitHub account before committing, then CI starts now.
I'm sorry for my misunderstanding.