button: raise from parent exception

This fixes a PyLint warning:

  W0707: Consider explicitly re-raising using the 'from' keyword
  (raise-missing-from)

Author: ktdreyer

adafruit_bluefruit_connect/button_packet.py

@@ -71,8 +71,8 @@ def __init__(self, button, pressed):
         # This check will catch wrong length and also non-sequence args (like an int).
         try:
             assert len(button) == 1
-        except:
-            raise ValueError("Button must be a single char or byte.")
+        except Exception as err:
+            raise ValueError("Button must be a single char or byte.") from err
 
         self._button = button
         self._pressed = pressed