Update for next preview version

Author: christophwille

.github/workflows/dotnet.yml

@@ -16,8 +16,8 @@ jobs:
     env:
         Solution: '**/ICSharpCode.AvalonEdit.sln'
         BuildPlatform: 'Any CPU'
-        BuildVersion: '6.1.0'
-        NupkgVersion: '6.1.0'
+        BuildVersion: '6.2.0'
+        NupkgVersion: '6.2.0-preview1'
     steps:
     - uses: actions/checkout@v2
     - name: Update project version

ChangeLog.md

@@ -1,8 +1,11 @@
 Note: this changelog only lists major changes and fixes for major bugs. For a complete list of changes, see the git log.
 
+tbd: AvalonEdit 6.2-preview1
+* tbd
+
 2021/03/08: AvalonEdit 6.1.0
 * https://github.com/icsharpcode/AvalonEdit/compare/v6.0.1...v6.1.0
-* 
+
 2020/09/07: AvalonEdit 6.1 Preview 1
 * https://github.com/icsharpcode/AvalonEdit/compare/v6.0.1...v6.1-preview1