requirements: ensure safe version of PyYAML >= 5.4 (CVE-2020-1747)

PyYAML versions 5.1–5.3.1 are vulnerable to CVE-2020-1747, which allows
arbitrary code execution through yaml.FullLoader. While PyYAML 5.4+
patches this, the dependency specification (pyyaml >= 5.1) doesn't
guarantee a safe version. Let's increase the requirement to version
5.4 to ensure a safe version of is used.

This patch is based on suggestions from:
"YanTong C <chyeyantong03@gmail.com>"

Change-Id: I901c76c59e9c1bab030eab81038e04a475b32510

README.md

@@ -97,7 +97,7 @@ Please install the following dependencies:
  - pyscard
  - pyserial
  - pytlv
- - pyyaml >= 5.1
+ - pyyaml >= 5.4
  - smpp.pdu (from `github.com/hologram-io/smpp.pdu`)
  - termcolor
 

requirements.txt

@@ -6,7 +6,7 @@ jsonpath-ng
 construct>=2.10.70
 bidict
 pyosmocom>=0.0.12
-pyyaml>=5.1
+pyyaml>=5.4
 termcolor
 colorlog
 pycryptodomex

setup.py

@@ -26,7 +26,7 @@ setup(
         "construct >= 2.10.70",
         "bidict",
         "pyosmocom >= 0.0.12",
-        "pyyaml >= 5.1",
+        "pyyaml >= 5.4",
         "termcolor",
         "colorlog",
         "pycryptodomex",