fix: make examples runnable

Author: AlexanderPrendota

examples/05_stdlib/01_letFunction.md

@@ -41,6 +41,7 @@ fun main() {
 3. Uses a null-safe call, so `let` and its code block are executed only on non-null values.   
 
 `let` can also be called on a result of another function execution:
+
 <div class="language-kotlin" theme="idea" data-min-compiler-version="1.3">
 
 ```kotlin

examples/05_stdlib/03_filter.md

@@ -1,6 +1,7 @@
 # filter
 
 *filter* function enables you to filter collections. It takes a filter predicate as a lambda-parameter. The predicate is applied to each element. Elements that make the predicate `true` are returned in the result collection.
+
 <div class="language-kotlin" theme="idea" data-min-compiler-version="1.3">
 
 ```kotlin