doc: fix typo in the diagnostics guide

Change-Id: Ib1b93e55788168b574badeb84d0e6c4f3795055e
Reviewed-on: https://go-review.googlesource.com/62510Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/diagnostics.html

@@ -103,8 +103,8 @@ production.
 
 <p>
 You may want to periodically profile your production services.
-Escpeically in system with many replicas of a single process, selecting
-a random replica periodically is safe option.
+Especially in a system with many replicas of a single process, selecting
+a random replica periodically is a safe option.
 Select a production process, profile it for
 X seconds for every Y seconds and save the results for visualization and
 analysis; then repeat periodically. Results may be manually and/or automatically