Context argument to GraphQL#execute() should be explicit in next breaking version

The reference implementation now has an explicit context value that is separate from the root value. So in that implementation, GraphQL#execute() now looks like:

export function execute(
  schema: GraphQLSchema,
  documentAST: Document,
  rootValue?: mixed,
  contextValue?: mixed,
  variableValues?: ?{[key: string]: mixed},
  operationName?: ?string
): Promise<ExecutionResult> {

We should probably follow in our next breaking version.

[andimarek]

This is the proposal:

• We will add a root object: This will be presented as root to DataFetchers
• root will be the source object for the first query

This is a breaking change.

[andimarek]

the PR is merged and will be in the next release