Fix the security vulnerability

Signed-off-by: Vadim Markovtsev <vadim@sourced.tech>

requirements.txt

@@ -2,7 +2,7 @@ clint>=0.5.1,<1.0
 matplotlib>=2.0,<4.0
 numpy>=1.16.0,<2.0
 pandas>=0.20.0,<1.0
-PyYAML>=3.12,<4.0
+PyYAML>=4.2b1,<5.0
 scipy>=0.19.0,<2.0
 protobuf>=3.5.0,<4.0
 munch>=2.0