fix: typo in let.md

* fix typo in let.md

* fix typo in let.md

Author: abelkov

examples/06_scope_functions/01_let.md

@@ -12,7 +12,7 @@ fun customPrint(s: String) {
 
 fun main() {
 //sampleStart
-    val empty = "testKotlin".let {         // 1
+    val empty = "test".let {               // 1
         customPrint(it)                    // 2
         it.isEmpty()                       // 3
     }