tour: add missing n in significance

Fixes bug 10694

Change-Id: Iaf0c8d5d93656cfd8e4ad9762ee4e1cce0bf8496
Reviewed-on: https://go-review.googlesource.com/9639
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/content/welcome.article b/content/welcome.article
index 9ce7d12..05b5f99 100644
--- a/content/welcome.article
+++ b/content/welcome.article
@@ -72,7 +72,7 @@
 #appengine: 
 #appengine: There are limitations to the programs that can be run in the playground: 
 #appengine: 
-#appengine: - In the playground the time begins at 2009-11-10 23:00:00 UTC (determining the sigificance of this date is an exercise for the reader). This makes it easier to cache programs by giving them deterministic output.
+#appengine: - In the playground the time begins at 2009-11-10 23:00:00 UTC (determining the significance of this date is an exercise for the reader). This makes it easier to cache programs by giving them deterministic output.
 #appengine: 
 #appengine: - There are also limits on execution time and on CPU and memory usage, and the program cannot access external network hosts. 
 #appengine: