Update mutations.rst

[sweenr]

I believe the [1] was ommitted from the from_global_id call as that method returns a tuple of type and id, of which we're only interested in the id here. Took me half a day to figure out why this code wasn't working today. See function def here: https://github.com/graphql-python/graphql-relay-py/blob/master/graphql_relay/node/node.py#L67

[coveralls]

Coverage remained the same at 92.718% when pulling d06217d on sweenr:patch-1 into 0916e03 on graphql-python:master.

[clarkmoody]

While we're here, the same code example starts with

import graphene import relay, DjangoObjectType
from graphql_relay import from_global_id

This should probably be expanded to

import graphene
from graphene import relay
from graphene_django import DjangoObjectType
from graphql_relay import from_global_id

[sweenr]

@clarkmoody That's a good point, thanks for catching that. That was something else I dealt with yesterday. I can make that fix as well.