Fix old description about GORP_TEST_DIALECT in README.md
Fix old description about GORP_TEST_DIALECT in README.md

mousesun/gorp,kevinc0825/gorm,evenco/gorp,kimxilxyong/gorp,cortex/gorp,mousesun/gorp,kimxilxyong/gorp,go-gorp/gorp,go-gorp/gorp,losinggeneration/gorp,GeertJohan/gorp,gabelula/gorp,yp-engineering/gorp,yp-engineering/gorp,evenco/gorp,GeertJohan/gorp,kevinc0825/gorm,cortex/gorp,gabelula/gorp,losinggeneration/gorp