Fix some icons not displayed on UIExamples' "Icons and Images" (PHUIIconExample) page

Summary:
Fix three typos in icon names

Closes T15454

Test Plan: Go to /uiexample/view/PHUIIconExample/ before and after applying the change; compare icons displayed for fa-codiepie, fa-user-o, fa-thermometer-0

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15454

Differential Revision: https://we.phorge.it/D25280