chore(.gitignore): ignore fleet & code rush (dotnet#8243)

Author: KevinZonda

.gitignore

@@ -6,10 +6,19 @@ project.lock.json
 nupkg/
 
 # Visual Studio Code
-.vscode
+.vscode/
 
 # Rider
-.idea
+.idea/
+
+# Visual Studio
+.vs/
+
+# Fleet
+.fleet/
+
+# Code Rush
+.cr/
 
 # User-specific files
 *.suo
@@ -32,6 +41,3 @@ bld/
 msbuild.log
 msbuild.err
 msbuild.wrn
-
-# Visual Studio 2015
-.vs/