Bumped version to 2.7.0 (firebase#106)

Author: hiranya911

firebase_admin/__init__.py

@@ -24,7 +24,7 @@
 
 # Declaring module version as per https://www.python.org/dev/peps/pep-0396/#specification
 # Update this accordingly for each release.
-__version__ = '2.6.0'
+__version__ = '2.7.0'
 
 _apps = {}
 _apps_lock = threading.RLock()