Enforce insert_final_newline in the editorconfig.

.editorconfig

@@ -4,6 +4,7 @@ root = true
 charset = utf-8
 end_of_line = lf
 indent_style = tab
+insert_final_newline = true
 
 [*.{cpp,hpp,c,h,mm}]
 trim_trailing_whitespace = true