Fix gql typings

[Guillaumez]

It seems that the typings from v2.10.2 are not exactly as expected.

Based on what i see in the gql function, it seems that the literals parameter accepts an array of strings or a string.

[apollo-cla]

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[hwillson]

Thanks @Guillaumez - I'll add this in. We would like to change this to not be necessary, but we'll do that in a future release.

[dotansimha]

Awesome :) The changes in 2.10.2 were breaking for us (in graphql-code-generator), we had to change the function usage to be gql([str]) instead of gql(str). This seems to fix that :)

Thanks @Guillaumez !