Update free-courses-pt_BR.md (#3191)

free-courses-pt_BR.md

 ### Index
 
 * [Android](#android)
+* [Dart](#dart)
 * [Git](#git)
 * [Go](#go)
 * [Haskell](#haskell)
@@ -13,6 +14,11 @@
 * [Desenvolvedor Android Iniciante](https://www.udemy.com/desenvolvedor-android-iniciante/) - Gabriel Ferrari, Adriano Sacardo (Udemy)
 
 
+### Dart
+
+* [Curso de Dart Lang](https://www.udemy.com/curso-de-dart-lang-completo/) - Sthefane Soares (Udemy)
+
+
 ### Git
 
 * [Git e Github para iniciantes](https://www.udemy.com/git-e-github-para-iniciantes/) - Willian Justen de Vasconcellos (Udemy)