v0.8.2

New:

• assertXXXType() functions help ensure type-correct code using graphql (#570)
• Added toJSON() and inspect() methods on all GraphQL types for easier debugging (#578)
• ValidationContext types are exported (a17256b)

Fixes:

• Differentiate between input values with no default and with null default (#569)
• Improvements to Flow types in field resolvers (#573, #575, #577)