update target framework in porting guide

Author: jjw24

port-plugins.md

@@ -3,7 +3,7 @@
 ### Notes
 
 - When porting, please keep the author's commit history
-- Flow Launcher targets .Net Core 3.1, so plugins should also be upgraded to keep the continuity of future developments
+- Flow Launcher targets .Net 5, so plugins should also be upgraded to keep the continuity of future developments
 - All dll libraries used by the plugin should be outputted and included in the final build, to do this, set the attribute CopyLocalLockFileAssemblies in your project file to true
 
 ### Steps
@@ -12,7 +12,7 @@
 2. Use try convert tool from https://github.com/dotnet/try-convert
 3. Try-convert -w path-to-folder-or-solution-or-project
 4. May need to fix on the project file, a good template to follow is the [Explorer plugin](https://github.com/Flow-Launcher/Flow.Launcher/blob/dev/Plugins/Flow.Launcher.Plugin.Explorer/Flow.Launcher.Plugin.Explorer.csproj) project:
-	- fix <TargetFramework> to netcoreapp3.1
+	- fix <TargetFramework> to net5.0-windows
 	- set the output location as 'Output\Release\<name of the project>'
 	- add `<CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>` and `<AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>` to the csproj file
 	- bump version to 2.0.0 and fix up any missing attributes if neccessary