docs: Fix typo (#4649)

Noted while skimming through #4536.

Signed-off-by: Per Lundberg <[email protected]>

docs/root/configuration/http_filters/router_filter.rst

@@ -232,7 +232,7 @@ x-envoy-attempt-count
 ^^^^^^^^^^^^^^^^^^^^^
 
 Sent to the upstream to indicate which attempt the current request is in a series of retries. The value
-will be "1" on the initial request, incremeting by one for each retry. Only set if the
+will be "1" on the initial request, incrementing by one for each retry. Only set if the
 :ref:`include_attempt_count_header <envoy_api_field_route.VirtualHost.include_request_attempt_count>`
 flag is set to true.