fix of the namespace reference error

Author: xieguigang

src/RDev/vscode/DescriptionTooltip.vb

@@ -3,7 +3,6 @@ Imports System.Runtime.CompilerServices
 Imports System.Text
 Imports Microsoft.VisualBasic.ApplicationServices.Development.XmlDoc.Assembly
 Imports Microsoft.VisualBasic.ComponentModel.DataSourceModel
-Imports Microsoft.VisualBasic.Text
 Imports SMRUCC.Rsharp.Development
 Imports SMRUCC.Rsharp.Interpreter
 Imports SMRUCC.Rsharp.Interpreter.ExecuteEngine
@@ -13,6 +12,7 @@ Imports SMRUCC.Rsharp.Interpreter.ExecuteEngine.ExpressionSymbols.Closure
 Imports SMRUCC.Rsharp.Interpreter.ExecuteEngine.ExpressionSymbols.DataSets
 Imports SMRUCC.Rsharp.Runtime.Components
 Imports SMRUCC.Rsharp.Runtime.Interop
+Imports ASCII = Microsoft.VisualBasic.Text.ASCII
 
 Public Module DescriptionTooltip