adafruit_itertools_extra: Fix import

The import statement incorrectly referred to the package,
not the submodule, leading to the reported traceback

Testing performed: the user's testcase,
```
>>> from adafruit_itertools.adafruit_itertools import count
>>> from adafruit_itertools.adafruit_itertools_extras import take
>>> take(1, count(1, 5))
[1]
```

Closes: #3

Author: jepler

adafruit_itertools/adafruit_itertools_extras.py

@@ -76,7 +76,7 @@
 
 #pylint:disable=invalid-name,deprecated-lambda,keyword-arg-before-vararg
 
-import adafruit_itertools as it
+from . import adafruit_itertools as it
 
 __version__ = "0.0.0-auto.0"
 __repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_Itertools.git"