Remove golang 1.7 from CI test matrix
Remove golang 1.7 from CI test matrix

As staticcheck requires now golang 1.8 as minimum version, the easiest
solution was to side step that issue and simply stop testing on go 1.7.

ema/node_exporter,knweiss/node_exporter,prometheus/node_exporter,prometheus/node_exporter,derekmarcotte/node_exporter,siavashs/node_exporter,siavashs/node_exporter,bs-github/node_exporter,siavashs/node_exporter,Jean-Daniel/node_exporter,joehandzik/node_exporter,derekmarcotte/node_exporter,knweiss/node_exporter,bs-github/node_exporter,Jean-Daniel/node_exporter,Jean-Daniel/node_exporter,ema/node_exporter,joehandzik/node_exporter,bs-github/node_exporter,derekmarcotte/node_exporter,bs-github/node_exporter,prometheus/node_exporter,Jean-Daniel/node_exporter,knweiss/node_exporter,chosenken/node_exporter,ema/node_exporter,derekmarcotte/node_exporter,chosenken/node_exporter,chosenken/node_exporter,ema/node_exporter,knweiss/node_exporter,chosenken/node_exporter,siavashs/node_exporter,joehandzik/node_exporter,joehandzik/node_exporter