fix typo.

Author: ORiON-

problems/higher_order_functions/problem.md

@@ -5,9 +5,9 @@ A higher-order function is a function that does at least one of the following:
 
 All other functions are first order functions. [1]
 
-Unlike many other languages with imperative features, JavaScript allows you to utilise higher-order functions because it has "first-class functions". This means functions can be treated just like any other value in JavaScript: just like Strings or Numbers, Function values can be stored as variables, properties on objects or passed to other functions as arguments. Function values are actually Objects (inheriting from `Function.prototype`) so you can even add properties and store values on them, just like any regular Object.
+Unlike many other languages with imperative features, JavaScript allows you to utilize higher-order functions because it has "first-class functions". This means functions can be treated just like any other value in JavaScript: just like Strings or Numbers, Function values can be stored as variables, properties on objects or passed to other functions as arguments. Function values are actually Objects (inheriting from `Function.prototype`) so you can even add properties and store values on them, just like any regular Object.
 
-The key difference between Functions and other value types in JavaScript is the call syntax: if a reference to a function is followed by parens and some optional comma-separated values: `someFunctionValue(arg1, arg2, etc)`, then the  function body will be executed with the supplied arguments (if any).
+The key difference between Functions and other value types in JavaScript is the call syntax: if a reference to a function is followed by parens and some optional comma-separated values: `someFunctionValue(arg1, arg2, etc)`, then the function body will be executed with the supplied arguments (if any).
 
 In this exercise we're going demonstrate that functions can be passed as values by passing you a function as an argument.