Fix apnsservice._createBody() enforcing template wrap

When creating template registrations with apnsservice, the template is
always wrapped under a key aps. This commit fixes this similarly to
#1219.
Merge remote-tracking branch 'azure/dev' into fix-apns-template-format
Merge pull request #1225 from andwun/fix-apns-template-format

Fix apnsservice._createBody() enforcing template wrap