Fix content type for text files

Should use the TextContent

Telemachus/src/IOPageResponsibility.cs

@@ -88,7 +88,7 @@ private HTMLResponseContentType GetContentType(string extension)
                 contentTypes[".otf"] = new HTMLResponseContentType { contentType = HTMLContentType.BinaryContent, mimeType = "application/font-sfnt" };
                 contentTypes[".mp4"] = new HTMLResponseContentType { contentType = HTMLContentType.BinaryContent, mimeType = "video/mp4" };
                 contentTypes[".json"] = new HTMLResponseContentType { contentType = HTMLContentType.BinaryContent, mimeType = "application/json" };
-                contentTypes[".txt"] = new HTMLResponseContentType { contentType = HTMLContentType.BinaryContent, mimeType = "text/plain" };
+                contentTypes[".txt"] = new HTMLResponseContentType { contentType = HTMLContentType.TextContent, mimeType = "text/plain" };
                 contentTypes[""] = new HTMLResponseContentType { contentType = HTMLContentType.BinaryContent, mimeType = null };
 
             }