use the correct string type in the tainted-path examples

Author: erik-krogh

csharp/ql/src/Security Features/CWE-022/examples/TaintedPath.cs

@@ -6,7 +6,7 @@ public class TaintedPathHandler : IHttpHandler
 {
     public void ProcessRequest(HttpContext ctx)
     {
-        String filename = ctx.Request.QueryString["path"];
+        string filename = ctx.Request.QueryString["path"];
         // BAD: This could read any file on the filesystem.
         ctx.Response.Write(File.ReadAllText(filename));
     }

csharp/ql/src/Security Features/CWE-022/examples/TaintedPathGoodFolder.cs

@@ -6,7 +6,7 @@ public class TaintedPathHandler : IHttpHandler
 {
     public void ProcessRequest(HttpContext ctx)
     {
-        String filename = ctx.Request.QueryString["path"];
+        string filename = ctx.Request.QueryString["path"];
 
         string publicFolder = Path.GetFullPath("/home/" + user + "/public");
         string filePath = Path.GetFullPath(Path.Combine(publicFolder, filename));

csharp/ql/src/Security Features/CWE-022/examples/TaintedPathGoodNormalize.cs

@@ -6,7 +6,7 @@ public class TaintedPathHandler : IHttpHandler
 {
     public void ProcessRequest(HttpContext ctx)
     {
-        String filename = ctx.Request.QueryString["path"];
+        string filename = ctx.Request.QueryString["path"];
         // GOOD: ensure that the filename has no path separators or parent directory references
         if (filename.Contains("..") || filename.Contains("/") || filename.Contains("\\"))
         {