Change usage of gsub to delete, as per Code Climate/Rubocop recommendation (#1753)

app/lib/formatter.rb

@@ -15,7 +15,7 @@ class Formatter
     html = status.text
     html = encode(html)
     html = simple_format(html, {}, sanitize: false)
-    html = html.gsub(/\n/, '')
+    html = html.delete("\n")
     html = link_urls(html)
     html = link_mentions(html, status.mentions)
     html = link_hashtags(html)