Bump cryptography python module version

The requirements.txt mandates 2.4.x version of cryptography python
module which has an issue as it checks if the payload is an instance
of bytes which is actually a bytearray. This issue is fixed in 2.5
version, hence bump up minimum version to 2.5.

Signed-off-by: Devaraj Ranganna <devaraj.ranganna@arm.com>

Author: urutva

requirements.txt

@@ -26,5 +26,5 @@ cmsis-pack-manager>=0.2.3,<0.3.0
 pywin32==224;platform_system=='Windows'
 wmi==1.4.9;platform_system=='Windows'
 psutil==5.6.2
-cryptography>=2.4.x,<2.5
+cryptography>=2.5,<3
 Click>=7.0,<7.1