Add .env to .gitignore

[RyanofWoods]

Summary

This file is useful for testing:

• solidus_paypal_braintree/spec/support/gateway_helpers.rb

  Lines 8 to 15 in 920a4e7

  	public_key: ENV.fetch('BRAINTREE_PUBLIC_KEY', 'dummy_public_key'),
  	private_key: ENV.fetch('BRAINTREE_PRIVATE_KEY', 'dummy_private_key'),
  	merchant_id: ENV.fetch('BRAINTREE_MERCHANT_ID', 'dummy_merchant_id'),
  	merchant_currency_map: {
  	'EUR' => 'stembolt_EUR'
  	},
  	paypal_payee_email_map: {
  	'EUR' => ENV.fetch('BRAINTREE_PAYPAL_PAYEE_EMAIL', '[email protected]')

It was removed from the file here:

• f9dc06d

Checklist

Check out our PR guidelines for more details.

The following are mandatory for all PRs:

• I have written a thorough PR description.
• I have kept my commits small and atomic.
• I have used clear, explanatory commit messages.

The following are not always needed (cross them out if they are not):

- [ ] I have added automated tests to cover my changes.
- [ ] I have attached screenshots to demo visual changes.
- [ ] I have opened a PR to update the guides.
- [ ] I have updated the README to account for my changes.

[elia]

@RyanofWoods I'm ok with merging this, but wondering if it can be set on your machine level .gitignore instead 🤔