Travis tests for v2.5.3

CHANGES/v2.5.md

@@ -190,7 +190,7 @@ For users:
   - `Plumed` object can be used in context managers (e.g. `with plumed.Plumed() as p:`).
 - Precompiled binaries are available on Anaconda cloud on the [conda-forge channel](https://anaconda.org/conda-forge/plumed).
 
-## Version 2.5.3 (to be released)
+## Version 2.5.3 (coming soon)
 
 For users:
 - Fixed a bug with \ref CONVERT_TO_FES and periodic variables, see \issue{441}