websocket: fix a minor grammar issue in a comment.
websocket: fix a minor grammar issue in a comment.

Fixes golang/go#10881

Change-Id: I9f16dd0425d4e3c4a05530411eb29a7193a9d242
Reviewed-on: https://go-review.googlesource.com/10621
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

veliamsli/net,muzining/net,cmars/tools,cmars/tools,flowlo/go-net,subuk/net,cesanta/goxnet,raboof/net,cmars/tools,albertjin/golang-net,albertjin/golang-net,flowlo/go-net,w4ngyi/net,w4ngyi/net,golang/net,yangxianjun/net,DramaFever/golang.org-x-net,gomini/net,muzining/net,mckinney-subgraph/net,yangxianjun/net,kiip/net,cesanta/goxnet,raboof/net,veliamsli/net,zabawaba99/net,zabawaba99/net,dafyddcrosby/net,gomini/net,dafyddcrosby/net,kiip/net,subuk/net,DramaFever/golang.org-x-net,cmars/tools,mckinney-subgraph/net