Added missing sgmllib3k requirement to requirements.txt

requirements.txt

@@ -80,6 +80,7 @@ rsa==4.6
 Send2Trash==1.5.0
 sentry-sdk==0.19.5
 service-identity==18.1.0
+sgmllib3k==1.0.0
 simplejson==3.17.2
 six==1.15.0
 soupsieve==2.0.1