Fix an IndexError edge case (#84)

There was an index error that occurs sometimes when running a custom edge tpu model. Disagreement between count and len(scores). Confirmed that this resolves the bug

pycoral/adapters/detect.py

@@ -234,4 +234,4 @@ def make(i):
         bbox=BBox(xmin=xmin, ymin=ymin, xmax=xmax,
                   ymax=ymax).scale(sx, sy).map(int))
 
-  return [make(i) for i in range(count) if scores[i] >= score_threshold]
+  return [make(i) for i in range(len(scores)) if scores[i] >= score_threshold]