[2.7] bpo-36502: Update link to UAX GH-44, the Unicode doc on the UCD. (GH-15808)

The link we have points to the version from Unicode 6.0.0, dated 2010.
There have been numerous updates to it since then:
  https://www.unicode.org/reports/tr44/GH-Modifications

Change the link to one that points to the current version. Also, use HTTPS..
(cherry picked from commit 64c6ac74)
Co-authored-by: Greg Price <gnprice@gmail.com>

Doc/library/unicodedata.rst

@@ -20,7 +20,7 @@ based on the :file:`UnicodeData.txt` file version 5.2.0 which is publicly
 available from ftp://ftp.unicode.org/.
 
 The module uses the same names and symbols as defined by the UnicodeData File
-Format 5.2.0 (see http://www.unicode.org/reports/tr44/tr44-4.html).
+Format 5.2.0 (see https://www.unicode.org/reports/tr44/).
 It defines the following functions: