os/exec: Update Cmd.Run() docs to reflect correct error return types
os/exec: Update Cmd.Run() docs to reflect correct error return types

Change-Id: I3fe92d74ff259abdf5d1fd28cdc822db88aae191
Reviewed-on: https://go-review.googlesource.com/39993
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

josharian/go,christopher-henderson/Go,golang/go,derekmarcotte/go,Cofyc/go,vsekhar/elastic-go,cloudflare/go,CAFxX/go,Cofyc/go,cloudflare/go,ImJasonH/go,vsekhar/elastic-go,golang/go,nawawi/go,polyverse-security/go,golang/go,polyverse-security/go,codestation/go,polyverse-security/go,ImJasonH/go,cloudflare/go,codestation/go,vsekhar/elastic-go,CAFxX/go,nawawi/go,ImJasonH/go,Cofyc/go,golang/go,akutz/go,golang/go,josharian/go,ImJasonH/go,CAFxX/go,vsekhar/elastic-go,codestation/go,CAFxX/go,josharian/go,akutz/go,derekmarcotte/go,ImJasonH/go,codestation/go,akutz/go,ImJasonH/go,Cofyc/go,golang/go,vsekhar/elastic-go,josharian/go,polyverse-security/go,derekmarcotte/go,derekmarcotte/go,cloudflare/go,polyverse-security/go,derekmarcotte/go,derekmarcotte/go,cloudflare/go,vsekhar/elastic-go,Cofyc/go,nawawi/go,akutz/go,codestation/go,CAFxX/go,polyverse-security/go,ImJasonH/go,derekmarcotte/go,cloudflare/go,golang/go,golang/go,akutz/go,polyverse-security/go,CAFxX/go,nawawi/go,akutz/go,Cofyc/go,nawawi/go,codestation/go,vsekhar/elastic-go,derekmarcotte/go,polyverse-security/go,josharian/go,nawawi/go,codestation/go,ImJasonH/go,akutz/go,josharian/go,Cofyc/go,josharian/go,cloudflare/go,CAFxX/go,akutz/go,CAFxX/go,josharian/go,cloudflare/go,vsekhar/elastic-go,Cofyc/go,nawawi/go,nawawi/go,codestation/go