Update version.py to 1.0.0rc0

Author: arnoegw

tensorflow_gnn/version.py

@@ -43,4 +43,4 @@
 # IMPORANT: Right after branching rX.Y, bump the main branch to X.(Y+1).0.dev1.
 # (Submit a change to the Source of Truth, get it out on the main branch asap.)
 
-__version__ = "1.0.0.dev3"
+__version__ = "1.0.0rc0"