nfd-status-http-server: erroneous <!DOCTYPE html> display

refs: #3019

Change-Id: I9b400446c12ed1b6b0899dced0d9b4aff8720d4c
diff --git a/tools/nfd-status-http-server-files/nfd-status.xsl b/tools/nfd-status-http-server-files/nfd-status.xsl
index d4fa89c..fcf128b 100644
--- a/tools/nfd-status-http-server-files/nfd-status.xsl
+++ b/tools/nfd-status-http-server-files/nfd-status.xsl
@@ -1,10 +1,9 @@
 <xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:nfd="ndn:/localhost/nfd/status/1">
-<xsl:output method="html" encoding="utf-8" indent="yes" />
+<xsl:output method="html" encoding="utf-8" indent="yes" doctype-system="about:legacy-compat"/>
 
 <xsl:template match="/">
-  <xsl:text disable-output-escaping='yes'>&lt;!DOCTYPE html></xsl:text>
   <html>
   <head>
   <title>NFD Status</title>