Add back UMD to npm builds

[soedirgo]

What kind of change does this PR introduce?

Patch update.

What is the current behavior?

When doing the TypeScript transition, we were assuming <script type="module"> is enough, but it seems being able to use it outside of module <script>s is still convenient, so we're adding it back (just for supabase-js).

What is the new behavior?

You can now use plain <script>s to import supabase-js from CDNs, like <script src="https://cdn.jsdelivr.net/npm/@supabase/supabase-js"></script> or <script src="https://unpkg.com/@supabase/supabase-js"></script> as before.

Then you can use it from a global supabase variable:

<script>
const { createClient } = supabase
supabase = createClient("url", "key")
...
</script>

Additional context

Fixes #278.

[kiwicopple]

Nice one Bobby 🙏

Fixes supabase/supabase#285

[kiwicopple]

🎉 This PR is included in version 1.0.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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