PyYAML 3.13 fixes some issues with Python 3.7 compatibility and was released in 2018.
@@ -0,0 +1 @@
+Bump minimum PyYAML to 3.13.
@@ -136,7 +136,7 @@ Twisted = {extras = ["tls"], version = ">=18.9.0"}
treq = ">=15.1"
# Twisted has required pyopenssl 16.0 since about Twisted 16.6.
pyOpenSSL = ">=16.0.0"
-PyYAML = ">=3.11"
+PyYAML = ">=3.13"
pyasn1 = ">=0.1.9"
pyasn1-modules = ">=0.0.7"
bcrypt = ">=3.1.7"