MAINT: update dependencies (lxml, PyYAML)

setup.py

@@ -166,12 +166,13 @@ def setup_package():
         packages=find_packages('src'),
         python_requires='>=3.6',
         package_dir={'': 'src'},
-        install_requires=['lxml>=3.6.4',
-                          'PyYaml>=3.12', 'future', 'PySocks>=1.6.7'],
+        install_requires=['lxml>=4.6.3',
+                          'PyYAML>=6.0', 'future', 'PySocks>=1.6.7'],
         extras_require={'keyring': ['keyring>=13.0.0'],
-                        'jsonschema': ['jsonschema==4.0.1']},
+                        'jsonschema': ['jsonschema>=4.4.0']},
         setup_requires=["pytest-runner>=2.0,<3dev"],
-        tests_require=["pytest", "pytest-cov", "coverage>=4.4.2", "jsonschema==4.0.1"],
+        tests_require=["pytest", "pytest-cov", "coverage>=4.4.2",
+                       "jsonschema>=4.4.0"],
         package_data={
             'caosdb': ['cert/indiscale.ca.crt', 'schema-pycaosdb-ini.yml'],
         },