feat: auto-switch to nightly

Automatically switch to nightly based on the version from Tutor core.
This means we will no longer have conflicts when we merge major releases
branches to the nightly branch.

tutorindigo/__about__.py

@@ -2,7 +2,7 @@
 __package_version__ = __version__
 
 # Handle version suffix for nightly, just like tutor core.
-__version_suffix__ = ""
+from tutor.__about__ import __version_suffix__
 
 if __version_suffix__:
     __version__ += "-" + __version_suffix__