Merge pull request #28 from siddacious/master

Nice! Thanks for catching and fixing.

Problem reproduced and fix verified using Trinket M0 onboard DotStar. This now produces a nice happy pink dotstar:
```python
Adafruit CircuitPython 3.0.2 on 2018-09-14; Adafruit Trinket M0 with samd21e18
>>> import adafruit_dotstar
>>> import board
>>> led = adafruit_dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1)
>>> led[0] = 0xEA6292
>>> 
```

Author: caternuson

adafruit_dotstar.py

@@ -157,7 +157,7 @@ def _set_item(self, index, value):
         if isinstance(value, int):
             rgb = (value >> 16, (value >> 8) & 0xff, value & 0xff)
 
-        if len(value) == 4:
+        if len(rgb) == 4:
             brightness = value[3]
             # Ignore value[3] below.
         else: