use released GLM in docs now

[kleinschmidt]

Ultimately we want to remove GLM-based things from the docs since it means we can't build docs with GLM-breaking changes, but for now this will allow docs to build.

[palday]

When GLM 2.0 comes out and drops its use of TableRegressionModel, then we can more clearly distinguish which package provides which functionality and focus on the stuff StatsModels actually vendors.

[kleinschmidt]

Ugh, the doctests that were updated in #272 were based on JuliaStats/GLM.jl#339 I think but that is not compatible with StatsModels 0.7 so I've had to revert all those doctest changes to the uglier ones.