Update request urllib3 (#464)

* requests: updated to version 2.27.1

* urllib3: updated to version 1.26.18

lib/urllib3/fields.py

@@ -1,4 +1,5 @@
 from __future__ import absolute_import
+
 import email.utils
 import mimetypes
 import re
@@ -26,7 +27,8 @@ def format_header_param_rfc2231(name, value):
     strategy defined in RFC 2231.
 
     Particularly useful for header parameters which might contain
-    non-ASCII values, like file names. This follows RFC 2388 Section 4.4.
+    non-ASCII values, like file names. This follows
+    `RFC 2388 Section 4.4 <https://tools.ietf.org/html/rfc2388#section-4.4>`_.
 
     :param name:
         The name of the parameter, a string expected to be ASCII only.
@@ -65,7 +67,6 @@ _HTML5_REPLACEMENTS = {
     u"\u0022": u"%22",
     # Replace "\" with "\\".
     u"\u005C": u"\u005C\u005C",
-    u"\u005C": u"\u005C\u005C",
 }
 
 # All control characters from 0x00 to 0x1F *except* 0x1B.