Markdownlint: Do not allow tabs in code blocks (#178)

.markdownlint.yaml

@@ -1,5 +1,3 @@
 ---
 MD004: false
-MD010:
-  code_blocks: false
 MD013: false

functional/index.md

@@ -7,7 +7,7 @@ Rust is an imperative language, but it follows many functional programming parad
 ```rust
 let mut sum = 0;
 for i in 1..11 {
-	sum += i;
+    sum += i;
 }
 println!("{}", sum);
 ```

idioms/pass-var-to-closure.md

@@ -40,7 +40,7 @@ let num3 = Rc::new(3);
 let num2_cloned = num2.clone();
 let num3_borrowed = num3.as_ref();
 let closure = move || {
-	*num1 + *num2_cloned + *num3_borrowed;
+    *num1 + *num2_cloned + *num3_borrowed;
 };
 ```
 

idioms/temporary-mutability.md

@@ -15,9 +15,9 @@ Using nested block:
 
 ```rust,ignore
 let data = {
-	let mut data = get_vec();
-	data.sort();
-	data
+    let mut data = get_vec();
+    data.sort();
+    data
 };
 
 // Here `data` is immutable.