validate feed keys used needs to allow periods

The recently introduced validate_feed_key [0] function
needs to account for cases when feed_id includes a
group. For example: "sign-quotes..signtext"

Fixes #71

[0]: 1e3d458

Author: flavio-fernandes

adafruit_io/adafruit_io.py

@@ -40,9 +40,9 @@ def validate_feed_key(feed_key):
     """
     if len(feed_key) > 128:  # validate feed key length
         raise ValueError("Feed key must be less than 128 characters.")
-    if not bool(re.match("^[a-z0-9-]+$", feed_key)):  # validate key naming scheme
+    if not bool(re.match("^[a-z0-9-\.]+$", feed_key)):  # validate key naming scheme
         raise TypeError(
-            "Feed key must contain lower case English letters, numbers, and dash."
+            "Feed key must contain lower case English letters, numbers, dash, and period."
         )