refactor(hugo): use strings.ReplacePairs for chained replacements

Adopt Hugo v0.158's strings.ReplacePairs in rss.xml and
parse_block_v3.html to replace nested replace calls.

modules/blox/layouts/rss.xml

@@ -17,7 +17,7 @@
     <description>{{ .Title | default site.Title }}</description>
     <generator>HugoBlox Kit (https://hugoblox.com)</generator>
     {{- with site.Language.Locale }}<language>{{.}}</language>{{end -}}
-    {{- with site.Copyright }}<copyright>{{ replace (replace . "{year}" now.Year) "&copy;" "©" | plainify }}</copyright>{{end -}}
+    {{- with site.Copyright }}<copyright>{{ strings.ReplacePairs . "{year}" now.Year "&copy;" "©" | plainify }}</copyright>{{end -}}
     {{- if not .Date.IsZero }}<lastBuildDate>{{ .Date.Format "Mon, 02 Jan 2006 15:04:05 -0700" | safeHTML }}</lastBuildDate>{{ end -}}
     {{- if .Scratch.Get "og_image" }}
     <image>