Provide Python 3 matplotlib

Once I get around to making numpy/scipy imported for Python 3, I'll
probably upgrade everything to Python 3 and drop Python 2 support from
the codebase, but I don't feel like doing that quite yet.

Change-Id: I164c8fbb3ce922a83b56e46f5cc432004c3a989c
diff --git a/debian/BUILD b/debian/BUILD
index 0cb12e7..9b7ad4d 100644
--- a/debian/BUILD
+++ b/debian/BUILD
@@ -55,7 +55,7 @@
     srcs = [
         "matplotlib_init.patch",
     ],
-    visibility = ["@matplotlib//:__pkg__"],
+    visibility = ["@matplotlib_repo//:__pkg__"],
 )
 
 filegroup(
@@ -182,6 +182,7 @@
         "python-matplotlib",
         "python-tk",
         "python3-matplotlib",
+        "python3-tk",
     ],
 )