slog-handler-guide/README.md: fix word duplication

Change-Id: Id17b4acd73e237813292a63112b30e915d652bd4
GitHub-Last-Rev: 2052832
GitHub-Pull-Request: #29
Reviewed-on: https://go-review.googlesource.com/c/example/+/550196
Reviewed-by: qiulaidongfeng <[email protected]>
Run-TryBot: qiulaidongfeng <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>
TryBot-Bypass: Jonathan Amsterdam <[email protected]>

Author: shalimski

slog-handler-guide/README.md

@@ -67,7 +67,7 @@ original remains unchanged.
 All subsequent output from `logger` will include those attributes.
 A logger's `With` method calls its handler's `WithAttrs` method.
 
-The `WithGroup` method is used to avoid avoid key collisions in large programs
+The `WithGroup` method is used to avoid key collisions in large programs
 by establishing separate namespaces.
 This call creates a new `Logger` value with a group named "g":