fix: Use caml_uint8_array_of_string in add_custom_section

While working on grain-lang#265 I noticed that I was getting errors on `caml_binaryen_add_custom_section` as `caml_array_of_string` was deprecated for `caml_uint8_array_of_string` this updates that. The reason this doesn't appear for us is because of our test suite never calls this function.

Author: spotandjake

src/module.js

@@ -122,11 +122,11 @@ function caml_binaryen_module_get_debug_info_filename(wasm_mod, index) {
 }
 
 //Provides: caml_binaryen_add_custom_section
-//Requires: caml_jsstring_of_string, caml_array_of_string
+//Requires: caml_jsstring_of_string, caml_uint8_array_of_string
 function caml_binaryen_add_custom_section(wasm_mod, name, contents) {
   return wasm_mod.addCustomSection(
     caml_jsstring_of_string(name),
-    caml_array_of_string(contents)
+    caml_uint8_array_of_string(contents)
   );
 }