modify tag to oci8

Signed-off-by: luoji <gunsluo@gmail.com>

Author: gunsluo

README.md

@@ -138,7 +138,7 @@ Oracle Driver is [oci8](https://github.com/mattn/go-oci8), it is not pure golang
 To install the library and command line program, use the following:
 
 ```bash
-go get -tags oracle -v github.com/rubenv/sql-migrate/...
+go get -tags oci8 -v github.com/rubenv/sql-migrate/...
 ```
 
 ```yml

sql-migrate/oracle.go

@@ -1,4 +1,4 @@
-// +build oracle
+// +build oci8
 
 package main