Update aiohttp-jinja2 requirement from ~=1.1.2 to ~=1.6 in /server

Updates the requirements on [aiohttp-jinja2](https://github.com/aio-libs/aiohttp_jinja2) to permit the latest version.
- [Release notes](https://github.com/aio-libs/aiohttp_jinja2/releases)
- [Changelog](https://github.com/aio-libs/aiohttp-jinja2/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiohttp-jinja2@v1.1.2...v1.6)

---
updated-dependencies:
- dependency-name: aiohttp-jinja2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

server/requirements.txt

@@ -1,7 +1,7 @@
 pyyaml~=5.1.1
 aiodns~=2.0.0
 aiohttp~=3.5.0
-aiohttp-jinja2~=1.1.2
+aiohttp-jinja2~=1.6
 aiosqlite~=0.10.0
 base58~=1.0.0
 indy_vdr~=0.3.4