Rename the query constant to have an underscore in it. (#241)

We got reports of conflicts with the old constant-name and symbols that
people were defining in their app.

generate/testdata/snapshots/TestGenerate-ListInput.graphql-ListInput.graphql.go

@@ -42,7 +42,7 @@ type __ListInputQueryInput struct {
 func (v *__ListInputQueryInput) GetNames() []string { return v.Names }
 
 // The query or mutation executed by ListInputQuery.
-const ListInputQueryOperation = `
+const ListInputQuery_Operation = `
 query ListInputQuery ($names: [String]) {
 	user(query: {names:$names}) {
 		id
@@ -56,7 +56,7 @@ func ListInputQuery(
 ) (*ListInputQueryResponse, error) {
 	req := &graphql.Request{
 		OpName: "ListInputQuery",
-		Query:  ListInputQueryOperation,
+		Query:  ListInputQuery_Operation,
 		Variables: &__ListInputQueryInput{
 			Names: names,
 		},