Cherry-pick patch from upstream for python3 fix

- Add weak dependency on python3-pyqtgraph (#1248735)

binwalk-2.0.0-fix-binvis-python3.patch

@@ -0,0 +1,15 @@
+This is part of upstream commit bfd3f88652f4c0eb055776238c1083e4e0916510
+
+diff --git a/src/binwalk/modules/binvis.py b/src/binwalk/modules/binvis.py
+index 4835537..a542cff 100644
+--- a/src/binwalk/modules/binvis.py
++++ b/src/binwalk/modules/binvis.py
+@@ -98,7 +98,7 @@ def _generate_plot_points(self, data_points):
+ 
+         # If the number of data points exceeds the maximum number of allowed data points, use a
+         # weighting system to eliminate data points that occur less freqently.
+-        if sum(data_points.itervalues()) > self.max_points:
++        if sum(data_points.values()) > self.max_points:
+ 
+             # First, generate a set of weight values 1 - 10
+             for i in range(1, 11):