Allow plot_action.py to support arrays

Change-Id: I5a57decc574ea707cd49fc2957a61489fda8f6b5
diff --git a/frc971/analysis/plotter.py b/frc971/analysis/plotter.py
index 6e3a879..0b43206 100755
--- a/frc971/analysis/plotter.py
+++ b/frc971/analysis/plotter.py
@@ -35,7 +35,7 @@
 
       # Create a legend label using the binary name (optional), the structure
       # name and the data search path.
-      label = key[1] + '.' + '.'.join(key[2])
+      label = key[1] + '.' + '.'.join(str(x) for x in key[2])
       if not no_binary_in_legend:
         label = key[0] + ' ' + label