Update pyproject.toml

Fixes #37

I update the toml file with the correct license
terms and costraining the aiida-core version
to be less then 3.0.0.

pyproject.toml

@@ -13,7 +13,7 @@ license = {file = 'LICENSE.txt'}
 classifiers = [
     'Development Status :: 4 - Beta',
     'Framework :: AiiDA',
-    'License :: OSI Approved :: MIT License',
+    'License :: Academic License',
     'Operating System :: POSIX :: Linux',
     'Operating System :: MacOS :: MacOS X',
     'Programming Language :: Python',
@@ -25,7 +25,7 @@ classifiers = [
 keywords = ['aiida', 'workflows']
 requires-python = '>=3.8'
 dependencies = [
-    "aiida-core>=2.2.2",
+    "aiida-core>=2.2.2,<3.0.0",
     "aiida-quantumespresso>=4.3.0",
     "aiida-phonopy>=1.1.3",
     "phonopy>=2.19.0,<3.0.0",