Update zlib version

Due to the release of zlib 1.3, zlib 1.2.13 is no longer available for download.

Author: ledsun

lib/ruby_wasm/build_system/product/zlib.rb

@@ -4,7 +4,7 @@ module RubyWasm
   class ZlibProduct < AutoconfProduct
     attr_reader :target
 
-    ZLIB_VERSION = "1.2.13"
+    ZLIB_VERSION = "1.3"
 
     def initialize(build_dir, target, toolchain)
       @build_dir = build_dir