database/sql: fix typo and wording
database/sql: fix typo and wording

Clean up the phrasing a little bit, make the comment fit in 80
characters, and fix the spelling of "guard."

Change-Id: I688a3e760b8d67ea83830635f64dff04dd9a5911
Reviewed-on: https://go-review.googlesource.com/34792
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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