fix .env.sample for new sqlx

Author: syphar

.env.sample

@@ -2,7 +2,7 @@ export DOCSRS_PREFIX=ignored/cratesfyi-prefix
 export DOCSRS_DATABASE_URL=postgresql://cratesfyi:password@localhost:15432
 
 # for local development with sqlx
-export DATABASE_URL="$DOCSRS_DATABASE_URL"
+export DATABASE_URL=postgresql://cratesfyi:password@localhost:15432
 
 export DOCSRS_LOG=docs_rs=debug,rustwide=info
 # To build with a PR that hasn't landed in a rust dist toolchain yet,