replace deprecated .Hugo by hugo function

themes/hugo-sustain/layouts/partials/head.html

@@ -15,7 +15,6 @@
         {{- if .Params.heading -}} {{- .Params.heading -}} {{- else -}} {{- .Site.Title -}} {{ print " | " }} {{- .Title -}} {{- end -}}
     {{- end -}}
 	</title>
-    {{ .Hugo.Generator }}
     <link rel="stylesheet" href="{{ .Site.BaseURL }}css/bootstrap-3.3.7.min.css" />
     <link rel="stylesheet" type="text/css" href="{{ .Site.BaseURL }}css/main.css" />
     {{- if .Params.highlight -}}
@@ -24,7 +23,7 @@
     <link rel="stylesheet" type="text/css" href="{{ .Site.BaseURL }}css/fontawesome/css/all.min.css" />
     <link rel="stylesheet" type="text/css" href="{{ .Site.BaseURL }}css/fonts.css" />
     {{ range .Site.Params.custom_css }}
-    <link rel="stylesheet" href="{{ $.Site.BaseURL}}{{ . }}?v={{ md5 $.Hugo.BuildDate }}" />
+    <link rel="stylesheet" href="{{ $.Site.BaseURL}}{{ . }}?v={{ md5 hugo.BuildDate }}" />
     {{ end }}
     {{ `<!--[if lt IE 9]>
 			<script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>