REPL now defaults to trying to use Svelte v3

[Conduitry]

Now that svelte@latest is v3, people visiting the v2 REPL without a version in their URL will get v3, which breaks everything. We should be explicit about fetching version 2 from unpkg.

[Conduitry]

And then while we're at it, we should update the github oauth app to use v2.svelte.dev instead of svelte.technology.

[Conduitry]

I think this takes care of the issue with what version of the compiler the REPL gets from unpkg:

diff --git a/src/routes/repl/index.html b/src/routes/repl/index.html
index 4975e83..de5a0a3 100644
--- a/src/routes/repl/index.html
+++ b/src/routes/repl/index.html
@@ -248,7 +248,7 @@
            return {
                examples,

-               version: query.version || 'latest',
+               version: query.version || '2',

                components: [],
                data: {},
@@ -277,7 +277,7 @@

            url: ({ version, gist, query, demo }) => {
                const params = [];
-               if (version !== 'latest') params.push(`version=${version}`);
+               if (version !== '2') params.push(`version=${version}`);
                if (gist) params.push(`gist=${gist.id}`);
                else if (demo) params.push(`demo=${demo}`);
                else if (query.gist) params.push(`gist=${query.gist}`);

[Conduitry]

Eesh we're also going to have to do something about the template that's used in the REPL for downloaded zips. Right now, update_template.sh is going to get the latest v3 template.

[Conduitry]

It might actually be best to just check an old v2 version of the template into this repo, because that's not really going to be getting updated any more.

[Conduitry]

Fixed.