Use correct day of week for arbitrary past expiration time

https://www.google.com/search?q=january+1+1990+day+of+week

Change-Id: Ie43c5197340b791c7db5c75568cb0258dce0fbc5

gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
index 5c9fd36..240a3a7 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
@@ -58,7 +58,7 @@
   static void setNotCacheable(HttpServletResponse res) {
     res.setHeader(HttpHeaders.CACHE_CONTROL, "no-cache, no-store, max-age=0, must-revalidate");
     res.setHeader(HttpHeaders.PRAGMA, "no-cache");
-    res.setHeader(HttpHeaders.EXPIRES, "Fri, 01 Jan 1990 00:00:00 GMT");
+    res.setHeader(HttpHeaders.EXPIRES, "Mon, 01 Jan 1990 00:00:00 GMT");
     res.setDateHeader(HttpHeaders.DATE, new Instant().getMillis());
   }