chore(deps): pin pyyaml to 3.4-compat version

Author: TheKevJames

setup.py

@@ -39,7 +39,9 @@
     ],
     tests_require=['mock', 'pytest'],
     extras_require={
-        'yaml': ['PyYAML>=3.10'],
+        # N.B. PyYAML 5.3 dropped support for Python 3.4... which we should
+        # also do...
+        'yaml': ['PyYAML>=3.10,<5.3'],
         ':python_version < "3"': ['urllib3[secure]'],
     },
     classifiers=[

tox.ini

@@ -15,7 +15,7 @@ usedevelop = true
 deps =
     mock
     pytest
-    pyyaml: PyYAML>=3.10
+    pyyaml: PyYAML>=3.10,<5.3
     cov3: coverage<4.0
     cov4: coverage>=4.0,<4.1
     cov41: coverage>=4.1,<5.0