Bump version to 2.2.8 for next round of development

Also, drop Python 3.3 and add Python 3.6 to the target Python
versions in setup.cfg

Signed-off-by: Alex Kavanagh <alex@ajkavanagh.co.uk>

setup.cfg

@@ -1,7 +1,7 @@
 [metadata]
 name = pylxd
 summary = python library for lxd
-version = 2.2.7
+version = 2.2.8
 description-file =
     README.rst
 author = Paul Hummer and others (see CONTRIBUTORS.rst)
@@ -17,9 +17,9 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.3
     Programming Language :: Python :: 3.4
     Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
 
 [files]
 packages =