Merge pull request #320 from alexandrebodin/allow-union-type-begining-pipe

Add support for leading vertical bar in union types

Author: robzhu

spec/Section 3 -- Type System.md

@@ -755,6 +755,28 @@ Union types have the potential to be invalid if incorrectly defined.
    Similarly, wrapping types may not be member types of a Union.
 2. A Union type must define one or more unique member types.
 
+#### Union type syntax
+
+Union types are defined by delimiting one or more types with a single vertical bar character `|`:
+
+```graphql
+union SearchResult = Photo | Person
+```
+
+You may also use a leading vertical bar:
+
+```graphql
+union SearchResult =
+  | Photo
+  | Person
+```
+
+Trailing delimiters are not supported:
+
+```!graphql
+union SearchResult = Photo | Person |
+```
+
 ### Enums
 
 GraphQL Enums are a variant on the Scalar type, which represents one of a