relax dependencies

[mjobin-mdsol]

Hi,

I wanted to give your gem a try, but simple gem install pubchem failed.

ox gem is locked to an ancient 2.2.x version
which includes a C extension that does not compile on my "recent" 4yr old mac.

current directory: /Users/majobin/.asdf/installs/ruby/3.0.6/lib/ruby/gems/3.0.0/gems/ox-2.2.4/ext/ox
make DESTDIR\= sitearchdir\=./.gem.20240520-12147-j5e5lq sitelibdir\=./.gem.20240520-12147-j5e5lq
compiling base64.c
compiling cache.c
cache.c:30:25: warning: implicit conversion from 'int' to 'char' changes value from 255 to -1 [-Wconstant-conversion]
    *d = (255 <= len) ? 255 : len;
       ~                ^~~
1 warning generated.
compiling cache8.c
compiling cache8_test.c
compiling cache_test.c
compiling dump.c
dump.c:604:27: error: incompatible function pointer types passing 'int (VALUE, VALUE, Out)' (aka 'int (unsigned long, unsigned long, struct _Out *)') to parameter of type 'int (*)(VALUE, VALUE, VALUE)' (aka 'int (*)(unsigned long, unsigned long, unsigned long)') [-Wincompatible-function-pointer-types]
            rb_hash_foreach(obj, dump_hash, (VALUE)out);
                                 ^~~~~~~~~

This triggered me to relax your dependencies and bump the version of this gem.