Fix numba version deprecation warning (#1118)

* Fix numba version parsing

* I think this is actually the bug

* Revert "I think this is actually the bug"

This reverts commit 655c6d0.

* packaging dependency

* Update setup.py

librosa/util/decorators.py

@@ -4,9 +4,10 @@
 '''Helpful tools for deprecation'''
 
 import warnings
+from packaging import version
 from decorator import decorator
 import numba
-if (numba.__version__ < '0.49.0'):
+if version.parse(numba.__version__) < version.parse('0.49.0'):
     from numba.decorators import jit as optional_jit
 else:
     from numba.core.decorators import jit as optional_jit

setup.py

@@ -38,6 +38,7 @@
     install_requires=[
         'audioread >= 2.0.0',
         'numpy >= 1.15.0',
+        'packaging >= 18',
         'scipy >= 1.0.0',
         'scikit-learn >= 0.14.0, != 0.19.0',
         'joblib >= 0.14',