Fix post_meta/reading_time (#427)

Author: lucasew

layouts/partials/post_meta.html

@@ -5,7 +5,7 @@
 {{- end }}
 
 {{- if (.Param "ShowReadingTime") -}}
-{{- $scratch.Add "meta" (slice (i18n "read_time" .ReadingTime | default (printf "%s min" .ReadingTime))) }}
+{{- $scratch.Add "meta" (slice (i18n "read_time" .ReadingTime | default (printf "%d min" .ReadingTime))) }}
 {{- end }}
 
 {{- with (partial "author.html" .) }}