[Enhancement] Add EmailVerified field for Apple's ID token

[althenlimzixuan]

Open issue:

[https://github.com//issues/557]

Close #557

[techknowlogick]

CI Fail is related, could you update the test mocks?

--- FAIL: Test_ToJSON (0.00s)
    session_test.go:40: 
        	Error Trace:	/home/runner/work/goth/goth/providers/apple/session_test.go:40
        	Error:      	Not equal: 
        	            	expected: "{\"AuthURL\":\"\",\"AccessToken\":\"\",\"RefreshToken\":\"\",\"ExpiresAt\":\"0001-01-01T00:00:00Z\",\"sub\":\"\",\"email\":\"\",\"is_private_email\":false,\"email_verified\":false}"
        	            	actual  : "{\"AuthURL\":\"\",\"AccessToken\":\"\",\"RefreshToken\":\"\",\"ExpiresAt\":\"0001-01-01T00:00:00Z\",\"sub\":\"\",\"email\":\"\",\"is_private_email\":false}"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-{"AuthURL":"","AccessToken":"","RefreshToken":"","ExpiresAt":"0001-01-01T00:00:00Z","sub":"","email":"","is_private_email":false,"email_verified":false}
        	            	+{"AuthURL":"","AccessToken":"","RefreshToken":"","ExpiresAt":"0001-01-01T00:00:00Z","sub":"","email":"","is_private_email":false}
        	Test:       	Test_ToJSON
FAIL
FAIL	github.com/markbates/goth/providers/apple	0.024s

[althenlimzixuan]

Test cases fixed.

[techknowlogick]

Woo! thanks for the PR.