Update version numbers

README.md

@@ -21,9 +21,9 @@ is specified right now, but best practices should emerge with implementation and
 
 ## Current version and branches
 
-The master branch (that you are looking at) is the 'stable' version of the spec. It is currently version 
-[0.5.1](https://github.com/radiantearth/stac-spec/milestone/5) of the specification. The 
-[dev](https://github.com/radiantearth/stac-spec/tree/dev) branch is where active development takes place, and may have inconsistent examples. 
+The master branch is the 'stable' version of the spec. It is currently version 
+[0.5.2](https://github.com/radiantearth/stac-spec/milestone/8) of the specification. The 
+[dev](https://github.com/radiantearth/stac-spec/tree/dev) branch, which you are looking at right now, is where active development takes place, and may have inconsistent examples. 
 Whenever dev stabilizes a release is cut and we merge dev in to master. So master should be stable at any given time.
 It is possible that there may be small releases in quick succession, especially if they are nice improvements that do 
 not require lots of updating.