chapter07 and chapter08: update methods for pyLDAvis, eli5 etc

pyLDAvis: 
`pyLDAvis.sklearn `
has been renamed to 
`pyLDAvis.lda_model`
https://github.com/bmabey/pyLDAvis/issues/245

eli5:
`from sklearn.utils.metaestimators import if_delegate_has_method`
has been renamed to 
`from sklearn.utils.metaestimators import available_if`
https://github.com/eli5-org/eli5/pull/44
