Constrain 'robotframework-requests' to versions <0.8.0

Robotframework request API was changed in a version 0.8.0.
It is not possible to use the newest version with the current
openbmc-test-automation codebase.
Therefore constrain 'robotframework-requests' version to <0.8.0.

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
Change-Id: I7485e8a86ee4b94704032f495309e05b53f6b379
diff --git a/requirements.txt b/requirements.txt
index 87924f2..588a094 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 robotframework
 requests
-robotframework-requests>=0.3.9
+robotframework-requests>=0.3.9,<0.8.0
 paramiko==2.0.9
 robotframework-sshlibrary
 robotframework-scplibrary