setup.py: depend on 'pyyaml', not 'pyaml'

In the pip namespace, 'pyaml' is "pretty-yaml", a YAML generator (but
not a YAML parser); 'pyyaml' (accessed with "import yaml"), a.k.a.
"PyYAML", is the YAML serialiser and reader we actually use.

Bump the minor version number per semantic versioning rules.  (One could
argue that we are "removing" pyaml (pretty-yaml) from our interface and
therefore a major version bump is required, but we weren't _actually_
using that module so I would argue that the introduction of 'pyyaml' is
the visible change.)

Thanks to Japheth Lim for identifying this issue.

tools/python-deps/setup.py

@@ -36,7 +36,7 @@ DEPS = [
     'pyelftools',
     'sh',
     'pexpect',
-    'pyaml>=5.1',
+    'pyyaml>=5.1',
     'jsonschema',
     'pyfdt',
     'cmake-format==0.4.5',
@@ -47,7 +47,7 @@ DEPS = [
 
 setup(
     name='sel4-deps',
-    version='0.3.1',
+    version='0.4.0',
     description='Metapackage for downloading build dependencies for the seL4 microkernel',
     url="https://sel4.systems",
     licence='BSD2',