GitilesView: Fix exception message

Change-Id: I42e29b042d0fbaa8a38c1ef16098188d25fe12ab

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

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/GitilesView.java b/gitiles-servlet/src/main/java/com/google/gitiles/GitilesView.java
index aae388c..10bfe96 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/GitilesView.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/GitilesView.java
@@ -280,7 +280,7 @@
     public Builder setExtension(String extension) {
       switch (type) {
         default:
-          checkState(extension == null, "cannot set path on %s view", type);
+          checkState(extension == null, "cannot set extension on %s view", type);
           // Fallthrough;
         case ARCHIVE:
           this.extension = extension;