Update isIsogram.md

snippets/isIsogram.md

@@ -8,7 +8,7 @@ Creates a function that accepts a string parameter and output whether its an iso
 - Use `String.toLowerCase()` to convert the string to lowercase letters.
 - Use `String.prototype.split()`, `String.prototype.indexOf()` and `Array.prototype.every()` to split the string into substrings, run a test for all the elements in that array and finally return the index of first occurence of a specified value in a string.
 - Function returns true if the string is an isogram (that is no letter is repeated) else returns false.
-- Returns false is called with no parameter.
+- Returns false if called with no parameter.
 
 ```js
 const isIsogram = (str = null) => {