Let's find characters in a string.
For this task, implement the getMiddleString()
function, which takes a string and returns middle character (or characters) as a string.
Please note: if the string length is even, return the two middle characters.
For example:
getMiddleString("hello") // "l"
getMiddleString("1234") // "23"
getMiddleString("(())") // "()"
getMiddleString("Bob") // "o"
getMiddleString("") // ""