fix(react): make the `Avatar` letter uppercase by default #394

Job	Run time
ʦ Typecheck (STATIC ANALYSIS) (lts/*)	8m 4s
🌳 ESLint (STATIC ANALYSIS) (lts/*)	9m 1s
💅 Storybook (lts/*)	6m 59s
👾 Unit Tests (lts/*)	7m 34s
🚧 Build (lts/*)	3m 27s
	35m 5s

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