Fix documentation example on JS library to include the explicit 'void' when declaring a function on JS side.

Author: juj

site/source/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.rst

@@ -335,7 +335,7 @@ As a simple example, consider the case where you have some C code like this:
 
 .. code-block:: c
 
-    extern void my_js();
+    extern void my_js(void);
 
     int main() {
       my_js();