fix: bump GitExtensions.Extensibility to 1.0.0 (#35)

Update GitExtensions.Extensibility to 1.0.0 to get rid of old plugins
with incorrect version handling.
Prepare for Git Extensions 7.

Author: gerhardol

appveyor.yml

@@ -3,7 +3,7 @@
 #---------------------------------#
 
 # version format
-version: 0.4.0.{build}
+version: 1.0.0.{build}
 
 #---------------------------------#
 #      environment configuration  #