Remove matplotlib version restriction

So far as I can tell the matplotlib version restriction (to 2.0.2) is not necessary and causes difficulties in conda (for me at least it triggers reinstallation of an older version which then fails to compile)

setup.py

@@ -82,7 +82,7 @@ setup(
         "librosa==0.6.2",
         "unidecode==0.4.20",
         "tensorboardX",
-        "matplotlib==2.0.2",
+        "matplotlib",
         "Pillow",
         "flask",
         # "lws",