Added createTypeName to ensure unique name for union types.

Author: michaek

packages/gatsby/src/schema/infer-graphql-type.js

@@ -290,7 +290,7 @@ function inferFromFieldName(value, selector, types): GraphQLFieldConfig<*, *> {
     // If there's more than one type, we'll create a union type.
     if (fields.length > 1) {
       type = new GraphQLUnionType({
-        name: `Union_${key}_${fields.map(f => f.name).join(`__`)}`,
+        name: createTypeName(`Union_${key}_${fields.map(f => f.name).join(`__`)}`),
         description: `Union interface for the field "${key}" for types [${fields
           .map(f => f.name)
           .join(`, `)}]`,