refactored exercism.io github references

CHANGELOG.md

@@ -299,7 +299,7 @@ Tweaked:
 
 ## v1.9.2 (2015-01-11)
 
-- [exercism.io#2155](https://github.com/exercism/exercism.io/issues/2155): Fixed problem with passed in config file being ignored.
+- [exercism#2155](https://github.com/exercism/exercism/issues/2155): Fixed problem with passed in config file being ignored.
 - Added first version of changelog
 
 ## v1.9.1 (2015-01-10)
@@ -419,15 +419,15 @@ Tweaked:
 
 ## v1.3.1 (2013-12-01)
 
-- [exercism.io#1039](https://github.com/exercism/exercism.io/issues/1039): Stopped clobbering existing files on fetch
+- [exercism#1039](https://github.com/exercism/exercism/issues/1039): Stopped clobbering existing files on fetch
 
 ## v1.3.0 (2013-11-16)
 
 - [7f39ee4](https://github.com/exercism/cli/commit/7f39ee4802752925466bc2715790dc965026b09d): Allow users to specify a particular problem when fetching.
 
 ## v1.2.3 (2013-11-13)
 
-- [exercism.io#998](https://github.com/exercism/exercism.io/issues/998): Fix problem with writing an empty config file under certain circumstances.
+- [exercism#998](https://github.com/exercism/exercism/issues/998): Fix problem with writing an empty config file under certain circumstances.
 
 ## v1.2.2 (2013-11-12)