Update CHANGELOG.md
Added entry for fixing
## 0.5.0 (2017-12-XX)
- Added: Command line `cache seed` and `cache purge` commands
- Added: More robust command line interface
+- Fixed: Possible Panic if a feature without an ID is added before a feature with an ID; when constructing Layers (#195)
Breaking changes:
- To use tegola as a web server, use the command `tegola serve --config=/path/to/config.toml`
