Increased latest version to 3.1.3b0 [skip ci]

README.rst

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-.. image:: https://img.shields.io/badge/docs-v3.1.2-yellow.svg
-   :target: https://www.idiap.ch/software/bob/docs/bob/bob.devtools/v3.1.2/index.html
+.. image:: https://img.shields.io/badge/docs-stable-yellow.svg
+   :target: https://www.idiap.ch/software/bob/docs/bob/bob.devtools/stable/index.html
 .. image:: https://img.shields.io/badge/docs-latest-orange.svg
    :target: https://www.idiap.ch/software/bob/docs/bob/bob.devtools/master/index.html
-.. image:: https://gitlab.idiap.ch/bob/bob.devtools/badges/v3.1.2/build.svg
-   :target: https://gitlab.idiap.ch/bob/bob.devtools/commits/v3.1.2
-.. image:: https://gitlab.idiap.ch/bob/bob.devtools/badges/v3.1.2/coverage.svg
-   :target: https://gitlab.idiap.ch/bob/bob.devtools/commits/v3.1.2
+.. image:: https://gitlab.idiap.ch/bob/bob.devtools/badges/master/build.svg
+   :target: https://gitlab.idiap.ch/bob/bob.devtools/commits/master
+.. image:: https://gitlab.idiap.ch/bob/bob.devtools/badges/master/coverage.svg
+   :target: https://gitlab.idiap.ch/bob/bob.devtools/commits/master
 .. image:: https://img.shields.io/badge/gitlab-project-0000c0.svg
    :target: https://gitlab.idiap.ch/bob/bob.devtools
 .. image:: https://img.shields.io/pypi/v/bob.devtools.svg

version.txt

-3.1.2
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+3.1.3b0
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