fix: paypal tokens request requires encoded redirect_uri

[Yizack]

Hello! This PR re-adds the encodeURIComponent to the redirect_uri when fetching tokens.

I noticed the utils refactor in #147 broke PayPal login because the redirect_uri encode was removed, I should have left a comment in the code when I made the PayPal provider PR (#108) saying that at the moment PayPal login for some reason requires encoding the redirect_uri when fetching the tokens.

For testing:

1. Login in sandbox mode https://developer.paypal.com/dashboard/applications/sandbox
2. Go to REST API apps Click on Default Application
3. Copy Client ID and Secret key 1
4. Create a .env file and add the credentials respectively NUXT_OAUTH_PAYPAL_CLIENT_ID and NUXT_OAUTH_PAYPAL_CLIENT_SECRET
5. Scroll down to the Features section, and enable Log in with PayPal
6. Click on the Advanced Settings link below the Log in with PayPal checkbox
7. Set Return URL to http://127.0.0.1:3000/auth/paypal
8. Scroll down, select the scopes Full Name and Email
9. Scroll down and enable Enable customers who have not yet confirmed their email with PayPal to log in to your app.
10. Click on the Save button
11. Go to https://developer.paypal.com/dashboard/accounts
12. Create a new Personal or Business account (Create a new one, I don't recommend using the default ones)
13. Click on the account name to see the credentials
14. Test PayPal Login with the credentials

[atinux]

Thank you for the fix and sorry about this regression 😬 v0.3.7 is released.

(cc @Barbapapazes to be more careful about future refactors)