Update CONTRIBUTING.md executable script template

Change `db` to type `*gorm.DB` to reflect latest version of gorm.
Remove re-declarations of `db, err`

CONTRIBUTING.md

@@ -27,26 +27,26 @@
 package main
 
 import (
-    _ "github.com/mattn/go-sqlite3"
+	_ "github.com/go-sql-driver/mysql"
-    _ "github.com/go-sql-driver/mysql"
+	"github.com/jinzhu/gorm"
-    _ "github.com/lib/pq"
+	_ "github.com/lib/pq"
-    "github.com/jinzhu/gorm"
+	_ "github.com/mattn/go-sqlite3"
 )
 
-var db gorm.DB
+var db *gorm.DB
 
 func init() {
-    var err error
+	var err error
-    db, err = gorm.Open("sqlite3", "test.db")
+	db, err = gorm.Open("sqlite3", "test.db")
-    // db, err := gorm.Open("postgres", "user=username dbname=password sslmode=disable")
+	// db, err = gorm.Open("postgres", "user=username dbname=password sslmode=disable")
-    // db, err := gorm.Open("mysql", "user:password@/dbname?charset=utf8&parseTime=True")
+	// db, err = gorm.Open("mysql", "user:password@/dbname?charset=utf8&parseTime=True")
-    if err != nil {
+	if err != nil {
-        panic(err)
+		panic(err)
-    }
+	}
-    db.LogMode(true)
+	db.LogMode(true)
 }
 
 func main() {
-    // Your code
+	// Your code
 }
 ```