Update concept exercises to pass the linter (#999)

Author: SleeplessByte

.prettierrc

@@ -1,5 +1,6 @@
 {
   "semi": true,
   "singleQuote": true,
-  "endOfLine": "lf"
+  "endOfLine": "lf",
+  "arrowParens": "always"
 }

concepts/array-analysis/introduction.md

@@ -1,7 +1,5 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 In JavaScript, an array is a list-like structure with no fixed length which can hold any type of primitives or objects, or even mixed types. The array elements can be accessed by their index. Arrays are also given a bunch of built-in methods. Some of these built-in methods can analyse the contents of the array. Many of the built-in functions that analyse the contents of an array, take a [`predicate`][predicate_in_programming] as argument.
 
 The built-in functions are meant to be used _instead of a `for` loop_ or the built-in `Array#forEach()`:

concepts/array-destructuring/introduction.md

@@ -1,7 +1,5 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 Javascript's array destructuring syntax is a concise way to extract values from an array and assign them to distinct variables.
 
 In this example, each value in the `numberOfMoons` array is assigned to its corresponding planet:

concepts/arrays/introduction.md

@@ -1,7 +1,5 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 In Javascript, an array is a list-like structure with no fixed length which can hold any type of primitives or ojects, even mixed types. The array elements can be accesed by their index.
 
 Example of an array declaration and accessing an element by index:

concepts/basics/introduction.md

@@ -1,7 +1,5 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 JavaScript is a dynamic language, supporting object-oriented, imperative, and declarative (e.g. functional programming) styles.
 
 There are a few primary ways to assign values to names in JavaScript - using variables or constants. On Exercism, variables are always written in [camelCase][wiki-camel-case]; constants are written in [SCREAMING_SNAKE_CASE][wiki-snake-case].

concepts/booleans/introduction.md

@@ -1,5 +1,3 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 A boolean represents one of two values: `true` or `false`. Logical operators (`!`, `&&`, `||`) are typically used with boolean values and they return a boolean value.

concepts/closures/introduction.md

@@ -1,7 +1,5 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 **Closures** are a programming pattern in JavaScript which allows variables from an outer [lexical scope][wiki-lexical-scope] to be used inside of a nested block of code. JavaScript supports closures transparently, and they are often used without knowing what they are.
 
 ```javascript

concepts/numbers/introduction.md

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 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 There are two different types of numbers in JavaScript:
 
 - `number`: a numeric data type in the double-precision 64-bit floating point

concepts/promises/introduction.md

@@ -1,7 +1,5 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
-
 The `Promise` object represents the eventual completion (or failure) of an
 asynchronous operation, and its resulting value.
 

concepts/recursion/introduction.md

@@ -1,3 +1,3 @@
 # Introduction
 
-TODO: the content below is copied from the exercise introduction and probably needs rewriting to a proper concept introduction
+TODO: add introduction for recursion concept