.stylelintignore: ignore minified CSS files

Change-Id: I239fd9bb2e851d5447f56be141ff646a24d20bb6
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/344398
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
diff --git a/.stylelintignore b/.stylelintignore
index 97796af..aa121f1 100644
--- a/.stylelintignore
+++ b/.stylelintignore
@@ -6,3 +6,5 @@
 # Worker stylesheet
 content/static/css/worker.css
 
+# Minified stylesheets
+*.min.css