Incorrect Reserved Expansion

[watuwo]

Valid UTF-8-percent-encoded code points must be preserved in reserved expansion. This implementation (Version: 4.1.1) fails the following test from https://github.com/uri-templates/uritemplate-test/blob/master/extended-tests.json:

{
  ...
  "Additional Examples 6: Reserved Expansion": {
    "variables" : {
      "id" : "admin%2F",
      ...
  },
  "testcases": [
    ["{+id}", "admin%2F"],
    ...
  ]
}

The correct/expected expansion is 'admin%2F', the actual expansion is 'admin%252F':

>>> from uritemplate import URITemplate, expand
>>> URITemplate('{+id}').expand(id='admin%2F')
'admin%252F'
>>> expand('{+id}', id='admin%2F')
'admin%252F'