Fix target_groups->static_configs in federation docs.
Fix target_groups->static_configs in federation docs.

open-falcon/open-falcon.github.io,du2016/prometheus-docs,tcolgate/docs,prometheus/docs,prometheus/docs,open-falcon/open-falcon.github.io,Cepave/openfalcon.io,chosenken/docs,prometheus/docs,tcolgate/docs,chosenken/docs,chosenken/docs,open-falcon/open-falcon.github.io,tcolgate/docs,Cepave/openfalcon.io,ddfreyne/prometheus-docs,ddfreyne/prometheus-docs,Cepave/openfalcon.io,du2016/prometheus-docs,du2016/prometheus-docs,chosenken/docs,ddfreyne/prometheus-docs,ddfreyne/prometheus-docs