fix 1272. Fixing aiohttp version to 3.6.2

library aioresponses 0.7.0 used only by unittests is failing
with the aiohttp version 3.7.x

Change-Id: Ic15dcaaf60b17a4c83b2c0ed6563eaa9cd0a4d98
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>