update basic types

Author: forax

guide/chapter01-basic_types.md

@@ -107,9 +107,10 @@ System.out.println("hello".length());
 ```
 
 to upper/lower case
+Locale.ROOT here ask for a result independent of the OS language
 ```java
-System.out.println("hello".toUpperCase());
-System.out.println("hello".toLowerCase());
+System.out.println("hello".toUpperCase(Locale.ROOT));
+System.out.println("hello".toLowerCase(Locale.ROOT));
 ```
 
 repeat the same pattern

jupyter/chapter01-basic_types.ipynb

@@ -202,15 +202,15 @@
 {
   "cell_type": "markdown",
   "metadata": {},
-  "source": ["to upper/lower case\n"]
+  "source": ["to upper/lower case\n", "Locale.ROOT here ask for a result independent of the OS language\n"]
 }
 ,
 {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
-  "source": ["System.out.println(\"hello\".toUpperCase());\n", "System.out.println(\"hello\".toLowerCase());\n"]
+  "source": ["System.out.println(\"hello\".toUpperCase(Locale.ROOT));\n", "System.out.println(\"hello\".toLowerCase(Locale.ROOT));\n"]
 }
 ,
 {