Fix doc typo (#6467)

requests/api.py

@@ -25,7 +25,7 @@ def request(method, url, **kwargs):
     :param cookies: (optional) Dict or CookieJar object to send with the :class:`Request`.
     :param files: (optional) Dictionary of ``'name': file-like-objects`` (or ``{'name': file-tuple}``) for multipart encoding upload.
         ``file-tuple`` can be a 2-tuple ``('filename', fileobj)``, 3-tuple ``('filename', fileobj, 'content_type')``
-        or a 4-tuple ``('filename', fileobj, 'content_type', custom_headers)``, where ``'content-type'`` is a string
+        or a 4-tuple ``('filename', fileobj, 'content_type', custom_headers)``, where ``'content_type'`` is a string
         defining the content type of the given file and ``custom_headers`` a dict-like object containing additional headers
         to add for the file.
     :param auth: (optional) Auth tuple to enable Basic/Digest/Custom HTTP Auth.