Localize post meta dates with time.Format function

* Use time.Format function (via `dateFormat` alias) to format post meta dates. It allows dates to be localized easily (with weekdays and months in the current language). Hugo v0.87.0 or later is required.
* Use old default format to preserve compatibility with older versions of Hugo

References:
- https://gohugo.io/functions/dateformat/
- https://gohugo.io/news/0.87.0-relnotes/

Author: Vimux

layouts/partials/post_meta/date.html

@@ -2,11 +2,11 @@
 <div class="meta__item-datetime meta__item">
 	{{ partial "svg/time.svg" (dict "class" "meta__icon") -}}
 	<time class="meta__text" datetime="{{ .Date.Format "2006-01-02T15:04:05Z07:00" }}">
-		{{- .Date.Format (.Site.Params.dateformat | default "January 02, 2006") -}}
+		{{- .Date | dateFormat (.Site.Params.dateformat | default "January 02, 2006") -}}
 	</time>
 	{{- if ne .Date .Lastmod }}
 	<time class="meta__text" datetime="{{ .Lastmod.Format "2006-01-02T15:04:05Z07:00" }}">(
-		{{- T "meta_lastmod" }}: {{ .Lastmod.Format (.Site.Params.dateformat | default "January 02, 2006") -}}
+		{{- T "meta_lastmod" }}: {{ .Lastmod | dateFormat (.Site.Params.dateformat | default "January 02, 2006") -}}
 	)</time>
 	{{- end -}}
 </div>