improve go mod support (#46)

Author: lunny

go.mod

@@ -1 +1,6 @@
-module "github.com/go-xorm/builder"
+module github.com/go-xorm/builder
+
+require (
+github.com/go-xorm/sqlfiddle v0.0.0-20180821085327-62ce714f951a
+github.com/stretchr/testify v1.3.0
+)

go.sum

@@ -0,0 +1,9 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-xorm/sqlfiddle v0.0.0-20180821085327-62ce714f951a h1:9wScpmSP5A3Bk8V3XHWUcJmYTh+ZnlHVyc+A4oZYS3Y=
+github.com/go-xorm/sqlfiddle v0.0.0-20180821085327-62ce714f951a/go.mod h1:56xuuqnHyryaerycW3BfssRdxQstACi0Epw/yC5E2xM=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=