Bump pyyaml and specify explicit FullLoader for yaml

Version for pyyaml has been restricted because it
has started to require an explicit loader for loading
yaml files. By appliying this commit, we can now remove
the restriction, since we explicitly specify the loader.

bellybutton/parsing.py

@@ -173,7 +173,7 @@ def parse_rule(rule_name, rule_values, default_settings=None):
 
 def load_config(fileobj):
     """Load bellybutton config file, returning a list of rules."""
-    loaded = yaml.load(fileobj)
+    loaded = yaml.load(fileobj, Loader = yaml.FullLoader)
     default_settings = loaded.get('default_settings')
     rules = [
         parse_rule(rule_name, rule_values, default_settings)

setup.py

@@ -12,7 +12,7 @@
     license='MIT',
     install_requires=[
         'astpath[xpath]==0.6.1',
-        'pyyaml>=3.12,<4.0',
+        'pyyaml>=4.0,<6.0',
         'lxml>=4.1.1',
     ],
     tests_require=['pytest>=3.1.2', 'future>=0.16.0'],