Create a function that returns the whole of the first sentence which contains a specific word. Include the full stop at the end of the sentence.
const str = "I have a cat. I have a mat. Things are going swell."
sentenceSearcher(str, "have") ➞ "I have a cat."
sentenceSearcher(str, "MAT") ➞ "I have a mat."
sentenceSearcher(str, "things") ➞ "Things are going swell."
sentenceSearcher(str, "flat") ➞ ""