Update PyYAML pin to latest version

Diff: yaml/pyyaml@5.1...5.2
Changelog: https://github.com/yaml/pyyaml/blob/master/CHANGES

Verified tests pass for me locally.

Closes aws#4749.

setup.cfg

@@ -10,7 +10,7 @@ requires-dist =
         docutils>=0.10,<0.16
         rsa>=3.1.2,<=3.5.0
         PyYAML>=3.10,<=3.13; python_version=="2.6" or python_version=="3.3"
-        PyYAML>=3.10,<5.2;python_version!="2.6" and python_version!="3.3"
+        PyYAML>=3.10,<5.3;python_version!="2.6" and python_version!="3.3"
         s3transfer>=0.2.0,<0.3.0
         argparse>=1.1; python_version=="2.6"
 

setup.py

@@ -45,7 +45,7 @@ def find_version(*file_paths):
     # Colorama removed support for EOL pythons.
     install_requires.append('colorama>=0.2.5,<=0.3.9')
 else:
-    install_requires.append('PyYAML>=3.10,<5.2')
+    install_requires.append('PyYAML>=3.10,<5.3')
     install_requires.append('colorama>=0.2.5,<0.4.2')