Move to gorp v2

This removes the following error, caused by the MySQL Dialect using a
'varchar' for all columns over 256 characters in length, instead of
'text' for the largest:

  2017/11/17 22:41:33 common_test.go:208: Error 1074: Column length too big for column 'Lua' (max = 21844); use BLOB or TEXT instead

internal/handlers/handlers.go

@@ -1,7 +1,7 @@
 package handlers
 
 import (
-	"gopkg.in/gorp.v1"
+	"gopkg.in/gorp.v2"
 	"log"
 	"net/http"
 	"path"

internal/handlers/tx.go

@@ -2,7 +2,7 @@ package handlers
 
 import (
 	"database/sql"
-	"gopkg.in/gorp.v1"
+	"gopkg.in/gorp.v2"
 	"strings"
 )