Update dependency: jinja2 < 3.0 and MarkupSafe < 2.0

Jinja2 and MarkupSafe have a plan to major release in the near future.
And it will introduce some changes for its APIs.  To lessen the noise
of the DeprecationWarnings, this pins the versions to current stable
release.

Author: tk0miya

setup.py

@@ -21,7 +21,8 @@
     'sphinxcontrib-htmlhelp',
     'sphinxcontrib-serializinghtml',
     'sphinxcontrib-qthelp',
-    'Jinja2>=2.3',
+    'Jinja2>=2.3,<3.0',
+    'MarkupSafe<2.0',
     'Pygments>=2.0',
     'docutils>=0.14,<0.18',
     'snowballstemmer>=1.1',