[1.8.x] Fixed #25056 -- Documented minimum version of jinja2 for testing.

Backport of ca58181bac from master

docs/internals/contributing/writing-code/unit-tests.txt

@@ -159,6 +159,7 @@ dependencies:
 
 *  bcrypt_
 *  docutils_
+*  jinja2_ 2.7+
 *  numpy_
 *  Pillow_
 *  PyYAML_
@@ -192,6 +193,7 @@ associated tests will be skipped.
 
 .. _bcrypt: https://pypi.python.org/pypi/bcrypt
 .. _docutils: https://pypi.python.org/pypi/docutils
+.. _jinja2: https://pypi.python.org/pypi/jinja2
 .. _numpy: https://pypi.python.org/pypi/numpy
 .. _Pillow: https://pypi.python.org/pypi/Pillow/
 .. _PyYAML: http://pyyaml.org/wiki/PyYAML

tests/requirements/base.txt

@@ -1,6 +1,6 @@
 bcrypt
 docutils
-jinja2
+jinja2 >= 2.7
 # move to py2.txt when dropping Python 3.2
 mock
 numpy