Fix hash syntax in swagger schemas

[johannesengl]

**Issue #146

Summary

The following hash syntax being used in notification_schema.rb and subscription_schema.rb schemas causes a syntax error on ruby 2.1

$ruby -e "h = {\"key\": \"value\"}; puts h"
-e:1: syntax error, unexpected ':', expecting =>
h = {"key": "value"}; puts h
           ^
-e:1: syntax error, unexpected '}', expecting end-of-input
h = {"key": "value"}; puts h

Using the following syntax we get the hash as expected with a symbol as the key:

ruby -e "h = {key: \"value\"}; puts h"
{:key=>"value"}

[coveralls]

Coverage remained the same at 100.0% when pulling 34634aa on johannesengl:fix-swagger-schema-hash-syntax into 10488e6 on simukappu:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 34634aa on johannesengl:fix-swagger-schema-hash-syntax into 10488e6 on simukappu:master.

[simukappu]

LGTM.
Thank you for your contribution!