Write a function called countVowels that takes in a string and returns the count of vowels $($i$.$e$.,\text{'}$a$\text{'},\text{'}$e$\text{'},\text{'}$i$\text{'},\text{'}$o$\text{'},$ and $\text{'}$u$\text{'})$ in the string. For example, if the input string is "hello", the function should return $2.($use hint, if necessary$)$