Update version before release (#1274)

* update version to 1.3.1 before release

* revert

* update version before release

heat/core/version.py

@@ -5,7 +5,7 @@
 """Indicates Heat's main version."""
 minor: int = 3
 """Indicates feature extension."""
-micro: int = 0
+micro: int = 1
 """Indicates revisions for bugfixes."""
 extension: str = None
 """Indicates special builds, e.g. for specific hardware."""