database/sql: correctly spell constants
database/sql: correctly spell constants

Also add a link to more information about isolation levels as defined by the
SQL standard. Fixes #17682.

Change-Id: I94c53b713f4c882af40cf15fe5f1e5dbc53ea741
Reviewed-on: https://go-review.googlesource.com/32418
Reviewed-by: Daniel Theophanes <14db39248b80c6688f7e9808ba5055f2e56426f3@gmail.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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