version.txt version should be updated

[james-pearce-bath-ac]

The version.txt file currently contains the string "3.13 - unstable (installed from github)" for the 3.13 release tags. The use of the term unstable could give concerns to users. Would it make sense to insure the version text is updated with each release if the could is considered releaseable?

[torinfo]

@james-pearce-bath-ac I removed 'unstable' from the version.txt fiel in the master branch.
What we normally do, is use the zip files published on the community website and teh version.txt fiels in those zip files indicate the exact released version based on the github tags and commits.

The current version would be something like 3.13 (git v3.13.5-3-g30176d555)

I'll see whether we can update the version.txt file of master as well.