use `-Os` in `build_web.sh`

build_web.sh

@@ -4,4 +4,4 @@ rm -rf web/lib
 mkdir web/lib
 
 SRC=$(find src/ -name "*.cpp")
-em++ $SRC -Iinclude/ -fexceptions -O3 -sEXPORTED_FUNCTIONS=_pkpy_new_repl,_pkpy_repl_input,_pkpy_new_vm -sEXPORTED_RUNTIME_METHODS=ccall -o web/lib/pocketpy.js
+em++ $SRC -Iinclude/ -fexceptions -Os -sEXPORTED_FUNCTIONS=_pkpy_new_repl,_pkpy_repl_input,_pkpy_new_vm -sEXPORTED_RUNTIME_METHODS=ccall -o web/lib/pocketpy.js